One of the biggest claims made by the Brexit campaign was that we could leave the EU and in doing so save ourselves £350 million per week that could be spent on the NHS instead. Despite being thoroughly debunked at the time, some people have clung to this “promise” and were somewhat vocal in their displeasure when campaigners such as Nigel Farage backtracked the day after the referendum.

Michael Gove, another out-campaigner and currently campaigning to be the next prime minister, has suggested he will pay £100million per week across to the NHS. And although significantly lower than the campaign promise, this remains a significant sum of money.

Is this new promise worth any more than the first?

First think about where the original figure came from. The sum of £350m a week is based on the Treasury’s estimation of the gross amount the UK contributed to the EU last year, which was £17.8bn, or £342m a week.

This figure is purely hypothetical because since Margaret Thatcher negotiated Britain’s rebate in 1984, the UK has been required to pay significantly less than the 1% of national GDP that member states are normally expected to pay into the EU’s collective budget.

The same Treasury figures clearly show Britain’s EU budget rebate last year was £4.9bn. Deduct that from £17.8bn and you get £12.9bn – or £248m a week. This is the sum now recognised by the independent fact-checking organisation Full Facts.

Plus, as Prof Ian Begg of the London School of Economics notes, the rebate is deducted before any payment is made, so it was simply wrong – and arguably deliberately untruthful – to say Britain “sends the EU £350m a week”.

The Treasury actually remits around £100m less a week.

Even the lesser weekly sum of £248m does not fairly reflect the cost to the UK of EU membership, because it ignores EU spending on the UK. Last year, the Treasury estimated these receipts from Brussels at £4.4bn, money spent mainly in the private sector but also distributed by public bodies, to farmers and poorer parts of the UK, such as Cornwall and south Wales, both of which voted “Leave”.

As pointed out by InFacts the EU also injects money directly into the UK’s private sector, for example, for scientific research through programmes such as Horizon2020. The most recent figure for this, from 2013, is £1.4bn.

Deduct both the rebate (£4.9bn), which is never actually paid, and the money that is paid but sent back (£5.8bn), from the gross £17.8bn annual “membership fee” and you arrive at a net figure of £7.1bn.

This equates to £136m a week, less than 40% of the amount splashed on the battles but still enough to make good on Mr Gove’s promised £100 million, unless …

Both the Treasury and the Bank of England are now warning of difficult economic times ahead due to the market uncertainty because of the Leave vote.

The size of the UK annual economic activity was £1,800 billion in 2015. Just a 1% economic change is £18bn a year or £346 million per week.

So if as a result of the referendum, the economy contracts by just 1%, we will be £210million out of pocket. Forecasts before the referendum ranged from a contraction of 4-8% to the economy.

At this stage it will be a struggle to maintain the amount of money we are currently paying towards the NHS never mind increase it.