Sarah Wollaston
Sarah WollastonConservative Party

A senior Conservative MP has defected from the Vote Leave campaign to backing a Remain vote at the EU referendum, accusing the Brexit group of "post-truth politics".

Dr Sarah Wollaston, the chair of the influential Health Select Committee, also claimed the campaign's contentious £350m a week figure – of how much the UK sends to the EU – was inaccurate.

"I think right from the outset there are people within the Leave campaign who acknowledge in private that they know this is not true, but what they are trying to encourage is a discussion about the amount. Well, this is a kind of post-truth politics," she told BBC Radio 4's Today programme.

The move was welcomed by fellow Remain campaigner and shadow health secretary Heidi Alexander, who praised Wollaston for "calling out the nonsense" from Vote Leave on the NHS.

The defection form the former GP is undoubtedly a coup for the Remain campaign, with just over a fortnight to go before the 23 June vote, but it is unlikely to have any significant effect on the referendum result.

The media focus will switch to Boris Johnson on the night of the 9 June, as the chief Vote Leave spokesman takes part in a live EU referendum debate show on ITV alongside SNP leader Nicola Sturgeon.

ITV's first show on 7 June, which adopted a question and answer format, featured the pro-EU prime minister David Cameron and Ukip leader Nigel Farage. The hour-long programme attracted an average audience of four million viewers and a 19.7% share.

The latest opinion poll from YouGov, of more than 2,000 people between 5 and 6 June, put Remain one point ahead of Leave (43% versus 42%), with 11% of respondents undecided.

Vote Leave had not responded to a request for comment at the time of publication.