Electrifying the traditional London taxi for the modern age

Clipper Automotive's 100% electric London Black Cab conversion
Clipper Automotive's 100% electric London Black Cab conversion

“My parents always did things slightly differently,” says Dr Alex Howard. “We had a car stereo mounted in the wall of our kitchen. Because my dad was like ‘it’s the best solution – it’s really good, it’s got all the features, and it doesn’t take up too much space…’ For them, there was always an alternative way of doing things.”

We’re sitting in the office of Clipper Automotive; the company that Howard co-founded. And outside, in the cramped but pretty mews it calls home, sit two examples of what the company does – or, more accurately, will do.

They’re black cabs. LTI TX4s, to be precise, and to the untrained eye they look identical to the thousands still plying their trade on the streets beyond the London mews gates.

But these two have a small square cut out of the front grille, a flap behind which lurks a definitive clue as to the modifications beneath their skins. Because if you haven’t already guessed by now, these two TX4s have been converted to run on electricity.


Of course, if you’re a resident of or regular visitor to London, you’ll probably be aware, even if only dimly, that London’s taxis are changing. The TX4 is old hat now, in the process of being phased out in favour of the new LEVC TX, a range extended electric taxi.

Trouble is, the TX comes in at around £60,000, even for the base model, even after the Government’s plug-in taxi grant. And each time one is bought, a perfectly usable TX4 stands a high chance of going to the scrap man, given demand for them on the used market is not vast.

To the untrained eye, the cabs look identical to those still plying their trade on the streets of London
To the untrained eye, the cabs look identical to those still plying their trade on the streets of London

A Clipper Automotive conversion, by contrast, costs a fiver under £40,000, including the donor vehicle. Or environmentally-conscious cabbies can lease one for £230 a week. And of course, it prevents a TX4 from going to waste.

“The idea was tickling in my brain for a while,” says Howard. “It’s partly because I live in central London, I cycle everywhere because it’s the quickest way to get around. And I’ve got kids and, you know, data was coming out on air quality and just how much damage it was doing to people’s health and so on. And, cycling around London, the diesel taxi – the TX4 – seemed to me to be the single biggest polluting vehicle type on the road. And I couldn’t understand why they were still there. So I looked into it and it seemed quite viable to convert the TX4 to electric.”

Rewind a few years, and you would have found Howard working for BT – a job he left in order to do something closer to his passion for sustainability. “I actually got into sustainability in the built environment,” he says, “and I found it quite frustrating. It was just so depressing – it was just greenwashing, like, ‘this isn’t real’.”

Howard’s background is in engineering – manufacturing systems, to be precise – and so he felt a strong pull toward doing something that could make a more tangible difference. But it wasn’t until 2020, and the arrival of the Covid-19 pandemic, that he was able to work on his idea.

“I like to think I would’ve done it anyway,” he says. “Because it was already a side project – I’d ring-fenced two days a week to do it. But it was actually the pandemic that gave me the time to work on it.”

First steps

Together with co-conspirator Janusch Opperman, a software engineer with a passion for automotive technology, Howard set to work building the first prototype. Based on the TX4’s forerunner, the TXII, it featured the batteries and motor from a crashed Nissan e-NV200, which gave it just 24kWh.

It was enough to prove the concept, however, and with it completed the pair were able to obtain a grant from Innovate UK, a Government-backed innovation fund, via the Niche Vehicle Network.

The batteries are split between the engine bay and the boot of the taxi, mounted in custom-built boxes that are steel framed
The batteries are split between the engine bay and the boot of the taxi, mounted in custom-built boxes that are steel framed

This spurred them to produce two more prototypes – the cars that sit before us – this time using recycled Nissan Leaf batteries, with a total of 40kWh apiece. Between them, these cars have now done 14,000 miles since they were converted. In short, then, they work.

Howard reckons the range should be around 150 miles – more than enough, in other words, to cover the average cabbie’s shift. “We’ve some feasibility work on going up to a 62kWh output using Tesla cells, which would give us a 200-mile range,” he says.

Either way, the batteries are split between the engine bay and the boot of the taxi, mounted in custom-built boxes that are steel framed and, in the boot at least, bolted to the chassis. Up front, the battery box sits atop a Tesla-sourced DC charger, with the motor then mounted within the transmission tunnel, feeding power to the rear wheels. The whole lot is controlled by a proprietary vehicle control unit, engineered by Clipper itself, which plugs into the taxi’s original wiring harness.

Howard is keen to point out that the conversion in its current form adds only 80kg to the taxi’s weight, a figure which the company intends to reduce further as it moves closer to production. Indeed, he even reckons he can reduce the weight of his electric taxi to below that of the diesel model.

The idea is to negate the need for significant suspension and brake upgrades, keeping the car as close as possible to standard specification, and giving it a fighting chance of complying with the stringent regulations that taxis are subject to.

“The battery boxes are kind of over-engineered,” Howard explains. “They’re made out of steel tube and they’re quite heavy even without the batteries. Initially we did that on purpose because I wanted to be really confident that the boxes were bulletproof.

“But we’ve since done finite element analysis of the crushing of these boxes, to see how they’d react in an impact, and we’re very happy about that. But there are ways to achieve that same strength with aluminium, with a lighter design of the structures and cases.

“Removing the spare tyre and replacing it with a kit – because when’s the last time you saw a black cab at the side of the road changing a tyre? Usually they call out a recovery service or take it to a garage – that will save more weight. I’m hoping to get it down to slightly under the original weight of the vehicle. That’ll be the target.”

London calling

There’s more work to come on these cars, then, which is why Howard is awaiting another round of fundraising to take the company to the next level. Importantly, this will enable the company to get the conversion approved by Transport for London (TfL), which will open up access to its biggest market.

“The TfL approval process is akin to a vehicle type approval,” he says. “It’s quite involved. It’s not as bad as it could be because we’re not doing everything from the bottom up, but they are requiring us to get independent verification against all the aspects of the vehicle that were needed for its original registration.”

'Even without the environmental argument, the Clipper conversion makes good sense,' says Robbins
'Even without the environmental argument, the Clipper conversion makes good sense,' says Robbins

As part of this, crash testing may even be a factor. “They haven’t said yet that they will require crash-testing. But they also haven’t said that they won’t,” Howard says with a laugh. “The worry is that these vehicles weren’t originally crash-tested to modern standards…” he adds.

But Howard is at least confident in the safety of his company’s installation. “We’ve designed the whole system to the UNECE Regulation 100, which is slightly more demanding than the statutory requirement in the UK.

“And then we get the Vehicle Certification Agency (VCA) to inspect each cab. They test the whole system for isolation resistance and all of the functional safety aspects of it.

“That report is then required by the DVSA, which then does its own roadworthiness checks on each individual vehicle – they check their brakes, suspension and weight and everything – all of the functional safety aspects. That enables us to get the IVA. So they’re independently inspected. I don’t think many retrofitters have gone to that extent.”

Fortunately, most of the regulators are more relaxed than TfL. “Councils like Oxford, Birmingham, and Edinburgh only need an IVA before they do their own compliance tests, which include, you know, whether you’ve got the right first aid kit in it and all that kind of stuff,” Howard says.

“Some councils have already given their approval. In fact, we’ve got a driver from Plymouth who might take one of the two we’ve already built. The other one is already licensed for use in Oxford.”

But what about the future? Surely there’s a finite number of TX4s and crashed Leafs that Clipper can use to carry out these conversions? Well, yes – but given Howard’s plans to scale the business, it comes as no great surprise that he’s already thought of that.

Waste not, want not

“There are still around 6,000 TX4s still in use in London. Each time I see one going to a scrap yard, I’m thinking ‘No!’,” he says with a rueful smile. “There’s still plenty of life left in these cars. Everything gets replaced on them to keep them in good order. TfL requires it. So we shouldn’t run out too soon.

“But I also know a guy who does LPG conversions, who got hold of about 80 unregistered TX4s, which he’s registered as 23-plate vehicles. They’re brand new – still got the plastic on the seats. We could convert one of those for sure, though of course it would be more expensive.

“But yes, as we scale, we will need to source new batteries. Urgently we can offer UK-sourced from Envision AESC factory, which should add about £2-3,000 to the cost of the conversion. We’re also looking into a more expensive spec with a 200-mile range from a Chinese supplier, but we don’t know when we will be offering this yet.

“Mind you, battery chemistry and module availability move on quite quickly, and we focus on modular tech and agile manufacturing. In other words, ask me again in six months, and we might have a different answer!”

The TX comes in at around £60,000, even for the base model
The TX comes in at around £60,000, even for the base model

Of course, with a brand-new taxi and batteries, the project starts to look less sustainable, which is why it’s geared more toward the idea of recycling and retrofitting. After all, this is an electric car which genuinely can claim to have been sustainably built - rejuvenating and reusing old taxis and batteries that would otherwise be scrapped.

The cost is relatively high, given these are, in part at least, used cars. But the Clipper cab is also much more affordable than a brand-new LEVC TX. And given the hybrid TX’s electric range is far shorter – and some drivers run theirs using the petrol engines most of the time – the Clipper conversion almost certainly works out to be a less polluting option.

Don’t be surprised to see Clipper-converted taxis hitting the streets near you soon, then. Just keep in mind you’ll have to look for that square cut-out in the grille to spot them.

Driving the Clipper TX4

Turn it on, stick it in drive, and go: It’s as simple as that. Though, admittedly, you do have to wait a couple of seconds between the second and third steps. When the additional matrix screen that Clipper has installed into the TX4’s dashboard says ‘ready’, you’re off.

Driving the Clipper cab really is simplicity itself. And it rapidly becomes clear why Dr Howard believes in this project.

The example we’re driving - an 07-plate - is showing more than 200,000 miles on the clock. Yet it drives almost perfectly. Yes, there’s a bit of slop in the steering around the dead-ahead, but TX4s are hardly bastions of steering precision in standard form. Otherwise, this example is free from nasty knocks or clunks, despite its mileage.

The brakes work brilliantly, the steering tracks straight and true. And with the Leaf motor powering you forward, performance is brisk, especially off the line. Indeed, electric powertrains lend themselves ideally to the sort of motoring most taxis do – lots of stop-start, lots of opportunities for regenerative braking to add charge to the battery, and quick responses at low speeds.

Granted, the Clipper doesn’t quite have the polish of a brand-new EV from a manufacturer. The motor’s a little noisier, and the drivetrain loads up with just a hint of a clunk. But after 10 minutes behind the wheel, you don’t really notice. And again, compared with the diesel TX4, the Clipper is quieter and smoother.

Not only will that make it more pleasant for passengers – it’ll mean drivers are less tired by the time their shifts are over, too. Even without the environmental argument, then, the Clipper conversion makes good sense.