Sir Keir Starmer's manifesto plans rely heavily on economy growing - but what if it doesn't?

Imagine a skyscraper: the tallest you've ever seen. Imagine it surrounded by other tall buildings - a cityscape of skyscrapers.

Now imagine a small semi-detached house standing in front of those buildings.

What you're picturing in your head is about the best visual approximation of the statistical difference between the fiscal plans from most of the manifestos this year - big, tall, towering financial commitments towards higher taxes and spending - and the Labour manifesto. That small semi-detached house is Labour's manifesto.

It is, at least in fiscal term, a tiddler.

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Now, there's a question we can get on to about whether Labour will actually end up keeping its fiscal figures anywhere close to those promised in its manifesto, but we now have them in black and white.

Broadly speaking there are two parts to the manifesto: the bit about day-to-day spending and the bit about green investment. Neither of them introduces any new policies we hadn't already heard about.

In short, Labour plans to raise taxes by £7.4bn by 2028/29 - mostly by tackling avoidance, clamping down on non-doms and forcing private schools to charge VAT. It plans to spend about £4.8bn of that money, which doesn't sound like all that much - and it isn't. Indeed, there are real questions about whether this is enough funding to keep public services functioning, given there are big real terms cuts pencilled in in the coming years.

Even so, it implies Labour will leave a £2.5bn buffer of safety in the public finances. In other words, it looks pretty cautious.

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But there's more to this than meets the eye, because then you've got to take into account the Green Prosperity Plan - the remnants of that £28bn investment promise Labour ditched not that long ago. This adds an extra £4.7bn of investment spending each year, balanced out by a further tax on oil and gas companies in the North Sea.

The upshot of all of this is that Labour are pledging to borrow more money - albeit money used for investment rather than day-to-day spending. They say this will be compatible with their fiscal rules, which is plausible - if you, again, assume they won't actually need to spend more on public services (which most people think they will).

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Manifesto checker: What the parties are promising

But the main takeaway isn't the minute detail of these policies - it's how small the whole shebang is. Consider: the scale of the Conservative's plans (I'm talking in this case about overall spending) is about £16bn a year by 2028/29. The scale of the Lib Dems' plans is £27bn (or £47bn when you include investment, which you really should).

The scale of the Labour manifesto plans is a mere £10bn or so each year. It is even more fiscally conservative than the Conservative manifesto.

And it's way, way, more small than the plans laid out by Jeremy Corbyn in the 2017 and 2019 manifestos. It implies a state that remains more or less the same size as today, with taxation ever so slightly higher than the current path - but not by much.

But that brings us back to that question: will it actually happen? Will Keir Starmer keep to these manifesto plans if Labour wins? His hope is that the economy begins to grow, delivering him the tax revenue he needs to improve public services. But what if it doesn't? The manifesto doesn't answer that question, but in due course it may prove impossible to avoid.