Boris Johnson has repeated the controversial claim that the UK will save £350m a week once it leaves the EU, and that a large proportion of this money should be spent on the NHS.
The figure was used by Leave campaigners in the run-up to the referendum but was later found to be "potentially misleading" by the UK statistics watchdog.
Remainers said the figure – printed on the side of a Leave campaign bus alongside the words, "Let's fund our NHS instead" – failed to take into account the full economic impact of being part of the EU, and of the rebate.
Even arch-Brexiteers such as Nigel Farage disassociated themselves from the sum.
But in a wide-ranging article for The Daily Telegraph, the foreign secretary chose to repeat the claim.
"Once we have settled our accounts, we will take back control of roughly £350 million per week," he wrote in Saturday's (16 September) edition.
"It would be a fine thing, as many of us have pointed out, if a lot of that money went on the NHS, provided we use that cash injection to modernise and make the most of new technology."
Johnson used the article to set out his vision for a post-Brexit Britain which enjoyed a low tax and low regulation economy, and which pays nothing to the EU for access to the single market.
The blueprint differs from the one set out by other Cabinet ministers, including the chancellor, who have stressed the need to remain close to the single market and potentially pay for access.
The foreign secretary also rounded on critics of Brexit "who think we are going to bottle it" and warned so-called Remoaners against treating the 17.4m Brexit voters as "fools".
He said Britain can be "the greatest country on earth" after leaving the EU, and that the country will have a better opportunity to improve its economy, solve the housing crisis and have an immigration policy that "suits the UK".
He also attacked Labour leader Jeremy Corbyn, saying his Brexit plan to remain in the single market and customs union is "incoherent" and a betrayal of pro-Brexit Labour voters.
He wrote: "In other words, he would make a complete mockery of Brexit, and turn an opportunity into a national humiliation. It would be the worst of both worlds, with the UK turned into a vassal state – taking direction from the EU, but with no power to influence the EU's decisions."
Corbyn, meanwhile, said Johnson's comments on the "fantasy" £350m figure was another attempt to "mislead the British public".
Johnson's article – which will likely reignite speculation among top Tories of his leadership ambitions – comes less than a week before Theresa May is due to give a pivotal Brexit speech in Florence.
She is expected to give an update on Brexit negotiations and "will underline the government's wish for a deep and special partnership with the European Union once the UK leaves the EU," the prime minister's spokesman said.