A senior Conservative MP has hit out at Boris Johnson over his continued insistence that an extra £350m could be invested in the NHS after Brexit.

Sarah Wollaston, the chair of the House of Commons Health Committee, said the Foreign Secretary’s use of the false statistic was “a disgrace” and “a deliberate deception”.

An additional £350m of investment in health care once Britain leaves the EU was a key pledge of the Leave campaign during the 2016 referendum and was famously plastered on the side of a bus, which Mr Johnson posed in front of.

However, the figure has been consistently and comprehensively debunked.

Despite this, Mr Johnson has continued to use the statistic and claimed earlier this week that it was actually an underestimate. He told The Guardian: “There was an error on the side of the bus. We grossly underestimated the sum over which we would be able to take back control.”

Dr Wollaston, a former GP, said Mr Johnson “should stop using that figure”.

She told BBC Five Live: “I feel it was entirely a deliberate deception [during the referendum campaign]. They knew that figure was incorrect but I had people repeatedly saying to me, ‘Well all that matters is that people remember a big number’.

“I found that shocking and I think it’s absolutely shocking that there are people continuing to use it.

She added: “[Mr Johnson] should stop using it. It’s a disgrace, and I feel very strongly about that.

“We need to be very careful about the way we use data and that goes for all of us in public life.”

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Last September, the chair of the UK Statistics Authority, Sir David Norgrove, wrote to Mr Johnson accusing him of a “clear misuse of statistics” for repeating the claim.

He said he was “surprised and disappointed” that the Foreign Secretary had continued to use the figure, which he said conflated the UK’s gross and net contributions to the EU.

While the UK currently pays around £350m per week to the EU, the figure does not take into account the money Britain receives from Europe in return. It also assumes that all payments currently made by the UK to the EU will cease once it leaves the union.

Mr Johnson’s latest use of the statistic prompted Sir Keir Starmer, the Shadow Brexit Secretary, to write to Sir David saying: “The £350m a week claim made by the Vote Leave campaign has been widely condemned as inaccurate and misleading.

“And yet, Mr Johnson has chosen to repeat this statement and expand on the claim even further. I do not believe this to be acceptable. I would therefore be grateful if you could make a statement on the accuracy of the Foreign Secretary’s most recent comments.”

Ms Wollaston said she supported Sir Keir’s letter and had herself written to the UK Statistics Authority over the figure.

She said: “We need to be clear that this figure, and the way it’s being used, is misleading and it was used deliberately in that way during the referendum campaign.”