The Tories’ campaign is a mess – their ‘attack’ on Labour spending is the proof

Something is wrong with the Tory campaign. It will not have helped that Jacob Rees-Mogg and Andrew Bridgen were supremely callous about Grenfell, or that a cabinet minister resigned after becoming embroiled in rape trial allegations – but it’s not these individual errors that suggest the Tory strategy is misfiring. Even the best strategists cannot stop these things from happening during election campaigns. All you can do is close them down fast and move on.

But there are signs that all is not well at the very heart of the campaign. Last week, someone in the Tory team briefed journalists that they would publish their economic attack on Labour, based upon Treasury costings of Labour’s spending promises. What happened instead was that Mark Sedwill, the most senior Treasury mandarin, refused to provide those costings, and Tory staffers had to hurriedly scramble together a dossier that was late and flimsy.

Why does this matter? Aside from Brexit, this economic message is the centrepiece of the Tory campaign. The fact that the Tories have screwed up this announcement suggests things are not working perfectly in Tory HQ.

One of the rituals of British elections is an early-morning press conference to unveil a poster featuring either a Labour tax bombshell or – in my case in 2001, 2005 and 2010 – massive Tory public spending cuts. Both are made in the same simple way: add up your opponent’s commitments, subtract any revenue-raising promises, and the result is the number you fight your campaign upon. The gold standard for any costing is to get the Treasury to do it. If ever you see government relying on a number from a party staff or some bloke at a thinktank, rather than their own official bean-counters, then you should regard it with extreme suspicion.

When I was in No 10, I spent the last six months in 2009 working with Treasury advisers and Labour party staff to get Treasury costings of Tory spending commitments and distil them into a clear attack. I say “working”, but what I really mean is arguing and fighting on a daily basis over every penny. Was it really a commitment, or just an aspiration? Were our assumptions too conservative, or not aggressive enough? Could we really claim this adds up to an attack on public spending, given that our own spending plans were looking dicey?

All of our attacks during the campaign – every poster, every leaflet, every Facebook ad, and the message we would be drilling into activists on the doorstep – would depend on this cuts message. We knew our workings would be pored over by our opponents, so there was a serious rigour to what we did. We needed to get the Treasury to cost it, either through ministerial requests or, if that didn’t work, by getting our own MPs to ask parliamentary questions designed to tease out the answer. We knew that if the Tories could start to knock down any of our calculations on the day of launch, then journalists would become even more doubtful about our claims, and the effectiveness of our flagship attack would be significantly reduced.

Related: Making up Labour spending figures may backfire on the Tories | Tom Kibasi

The Conservative Research Department, which was established by Neville Chamberlain and was regarded as an intellectual powerhouse under Keith Joseph during Margaret Thatcher’s tenure, always used to operate with this kind of academic rigour. However, its flagship work at this election contains not a single Treasury costing, repeatedly relies on assumptions (21 times, to be exact) and, when you probe the source to examine the basis for some of those assumptions, it feebly says, “CRD analysis available upon request.” In other words, they have had to rewrite the whole thing since Tuesday and have relied on dodgy back-of-an-envelope numbers that they don’t feel confident enough to share publicly.

There has also been talk of a disagreement between Johnson’s senior adviser, Dominic Cummings, and the chancellor, Sajid Javid, over whether this kind of attack is the right strategy, rather than focusing on Brexit. After all, the Tory strategy is to encourage wavering Labour voters in Midlands, northern and Welsh towns to vote for Brexit, rather than stick with Labour. So is it really a good idea to remind them that Labour stands for huge investment in popular things, such as free prescriptions and Sure Start, which the Tories would never fund?

Rachel Whetstone, who was political secretary to Michael Howard when he was leader of the Conservatives, once told me that the most underrated thing in politics was competence. For all the noise about Rees-Mogg and Alun Cairns, this somewhat nerdy issue about the Tories’ failure to get Treasury costings raises questions about the organisation and preparedness of their campaign. Not only did they fail to do their homework, but they briefed the lobby that they were ready, without any due diligence. And it could cost them votes: they may still have a healthy lead in the polls, but Labour are ticking back up.

• Theo Bertram is a former adviser to Tony Blair and Gordon Brown