Leaders of the cross-party campaign that persuaded the British people to leave the EU have dropped their pre-referendum pledge of a £350m-a-week spending bonanza for the NHS.

Many of those who headed the Vote Leave campaign, including its former chair, Labour MP Gisela Stuart, and Michael Gove, the Tory former justice secretary, are re-forming this weekend, creating a new pressure group called Change Britain.

Other top names involved in the organisation, which says it is being established to help “deliver the UK’s referendum result in the most effective way”, include former chancellor Nigel (Lord) Lawson, Digby Jones, former head of the CBI, and David (Lord) Owen, the former Labour foreign secretary.

But despite the NHS pledge having been at the heart of their message in the run-up to the 23 June vote, and displayed on the official Vote Leave battlebus, the Change Britain website made no mention of the NHS in its manifesto about how to make a success of Brexit.

Instead, Change Britain said on its “Brexit Means Brexit” page that any savings made as a result of no longer having to pay into the EU budget (assuming the UK leaves the single market) should be spent on guaranteeing “continued funding for farming, science, universities and poorer regions of the UK”. The website was taken down, although cached versions of its pages were still accessible through search engines.

Facebook Twitter Pinterest Liam fox told a Conservative reception the UK had grown ‘too fat’ on the successes of previous generations. Photograph: Andy Rain/EPA

Anna Soubry, the pro-Remain Tory MP and former minister for small business, said it was outrageous that the Leave campaigners had “peddled that lie” during the campaign and were now quietly abandoning it.

The Remain camp argued all along that it was wrong to claim that the UK sent £350m a week to Brussels as this is the gross figure and does not take account of the large sums of money that come back in EU farm and other subsidies, including structural funds and education and research grants. The idea that so much extra money could be guaranteed for the NHS post-Brexit was also challenged as totally unrealistic.

What has happened to the leave campaign's £350m pledge for the NHS? Read more

Soubry, a leading light in Open Britain, the successor to the Remain campaign, added: “They should all hang their heads in shame. There were many people, particularly in less wealthy areas, who were convinced by Leave’s claim that if we left the EU we would be able to pour millions more into the NHS. The danger now is these people will become even more disillusioned with all politicians because this lot misled them.”

Last weekend, prime minister Theresa May, speaking at the G20 summit in China, said she was unable to guarantee extra money for the health service post-Brexit, and came out against a points- based immigration system – which was the other central plank of the Brexit campaigners’ pitch to voters.

In an open letter, 30 Labour MPs – including former cabinet minister Ben Bradshaw, former shadow Europe minister Pat McFadden and ex-frontbenchers Emma Reynolds and Chuka Umunna – call on the Brexit campaigners to admit the NHS pledge was a lie.“ There should be no escaping this pledge for the Leave campaign – they cannot walk away from it now, disown it or pretend it never happened. They must either admit it was a lie and apologise to their voters, or justify it.”

On Saturday Downing Street made clear its annoyance with Liam Fox, the international trade secretary responsible for negotiating post-Brexit trade deals, who angered businesspeople by suggesting British executives would rather play golf than export their goods and services.

Fox, a former GP and staunch Eurosceptic, told a reception for the Thatcherite group Conservative Way Forward that the UK had grown “too fat” on the successes of previous generations. Downing Street issued a curt statement saying these were Fox’s private opinions.