LONDON, Feb 14 (Reuters) - Foreign minister Boris Johnson will appeal on Wednesday to those who he says are seeking to reverse the result of Britain's vote to leave the European Union, saying Brexit "is not grounds for fear but hope".

In the first of several speeches by government ministers that Prime Minister Theresa May hopes will set out a "road to Brexit", Johnson will try to unite a divided nation by urging Britons to rally around a vision for a better future outside the EU.

Johnson, a prominent Brexit campaigner, and the rest of May's team are under pressure from EU supporters who want Britain to keep the closest possible ties with the bloc, including remaining a member of the customs union. Brexit supporters say this would curb Britain's power to negotiate free trade agreements with other countries.

"I fear that some people are becoming ever more determined to stop Brexit... I believe that would be a disastrous mistake that would lead to permanent and ineradicable feelings of betrayal," Johnson will say, according to excerpts of his speech.

"I want to try today to anatomise at least some of those fears and to show to the best of my ability that they are unfounded, and that the very opposite is usually true: that Brexit is not grounds for fear but hope."

The speech in London is being billed by aides as a chance for Johnson, who is credited with persudading many Britons to vote to leave the bloc, to show a path for "an outward-facing, liberal, and global Britain following our exit from the EU".

FRUSTRATION

The foreign minister has become increasingly frustrated, his aides say, that what he sees as his legacy - a promise to return millions of pounds to Britain's state-funded health service - is being squandered by an indecisive May, weakened after losing the Conservative Party's majority in an election last June.

Instead he not only wants to go on the attack to show that Brexit, bogged down in difficult negotiations with Brussels, can be a success, but also to win over those who voted in the 2016 referendum to remain in the EU, his aides say.

"If we are to carry this project through to national success - as we must - then we must also reach out to those who still have anxieties," he will say.

"It is not good enough to say to Remainers – you lost, get over it; because we must accept that many are actuated by entirely noble sentiments, a real sense of solidarity with our European neighbours and a desire for the UK to succeed." (Reporting by Elizabeth Piper; Editing by Gareth Jones)