BORIS Johnson has set out a detailed vision for Britain's exit from the European Union that revives the widely-criticised claim Brexit could boost NHS coffers by £350 million a week.

Just six days before British Prime Minister Theresa May will set out her Brexit blueprint in a speech in Florence, the British Foreign Secretary has penned a 4,000 word article laying out his own path for a "glorious" future outside the bloc.

Britain should not pay for access to European markets and must seize the opportunity to reform the tax system to encourage investment, he said.

Continued membership the single market and customs union would make a "complete mockery" of the referendum result, Mr Johnson suggests.

The Foreign Secretary's decision to publicise his own Brexit strategy is likely to fuel speculation his leadership ambitions remain undimmed.

In the article for the Daily Telegraph, he insists Brexit will allow the UK to "be the greatest country on earth" and "our destiny will be in our own hands".

"This country will succeed in our new national enterprise, and will succeed mightily," he wrote.

The Leave campaign's most eye-catching pledge during the referendum campaign was a claim ending Britain's contributions to the EU would free up an extra £350 million a week that could be spent on the NHS.

But it was widely derided and in the weeks after the result, Mr Johnson and other campaigners, appeared to distance themselves from the promise.

In the article for the Telegraph, however, he said the UK would "roughly" be £350 million better off and it would be a "fine thing" if a lot of it went on the health service.

He wrote: "Once we have settled our accounts, we will take back control of roughly £350 million per week. 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...

"One of the advantages of investing in the NHS - if we combine that investment with reform - is that we can turbo charge the role of our health service in driving bioscience."

Critics warned there is "absolutely no chance" of the £350 million pledge being delivered and said Mr Johnson was untrustworthy.

Mr Johnson does not mention plans for a transition period after Britain leaves the bloc in March 2019 and argues there is no need to pay for market access.

"We would not expect to pay for access to their markets any more than they would expect to pay for access to ours," he said.

The Government should "seize the opportunity" of Brexit to reform our tax system to boost investment.

"Outside the EU there are obvious opportunities - in agriculture, fisheries, in the setting of indirect taxation," he said.

"At the stroke of a pen, the Chancellor will be able to cut VAT on tampons; often demanded by Parliament but - absurdly - legally impossible to deliver."

The UK should not slam the door on immigration but businesses must do more to give British youngsters a good start in life.

"We will have an immigration (system) that suits the UK, not slamming the door - but welcoming the talent we need, from the EU and around the world," he said.

"Of course we will make sure that business gets the skills it needs, but business will no longer be able to use immigration as an excuse not to invest in the young people of this country."

Free trade deals outside the EU could help lift billions out of poverty in developing parts of the world, Mr Johnson insisted.

Rules restricting foreign buyers from snapping up property could be imposed once Britain leaves the EU, he added.

"It is often pointed out that the price of housing in certain parts of London may be increased by buyers from overseas. But there is no point in putting any kind of tax on foreign buyers, because the inhabitants of 27 other countries cannot legally be treated as foreign."

British Labour's Chuka Umunna, leading supporter of Open Britain, which is campaigning for continued single market membership, said: "Boris Johnson had a chance to vote to deliver the £350 million extra a week for the NHS in February, and he refused to do so.

"He promised to guarantee the rights of EU citizens living in Britain, and nothing has happened. No one can trust a word he says.

"The £350 million a week promise was a fib, and there is absolutely no chance of it being delivered. Boris should be apologising for his disgraceful conduct in the referendum, not continually making the same impossible promises.

"He's like an old rocker who sings the same tunes, but they just don't sound right anymore. A period of silence on his part would be welcome."

Labour said the article exposed the divisions in Mrs May's top team.

A spokesman for Jeremy Corbyn said: "Boris Johnson has laid bare the conflicts at the heart of Theresa May's Government over Brexit and cut the ground from beneath the Prime Minister's authority.

"In the process he has exposed the Tories' real Brexit agenda - a race-to-the-bottom in regulation and corporate tax cuts to benefit the wealthy few at the expense of the rights of the rest of us.

"The Foreign Secretary even has the gall to dredge up the fantasy of £350 million a week extra for the NHS. The Prime Minister must spell out now how this will be paid for, or stand condemned for once again trying to mislead the British public."

PA Media