"If the Brexit Party comes out on top in a couple of weeks time, we must have a place at the negotiating table with the government to help put together our strategy".
He went on to say he would be prepared to "do a deal with the devil" for a Brexit which would see the United Kingdom leave the Customs Union, the single market, and the jurisdiction of the European Court of Justice.
"You would have lost the loyal middle of the Conservative Party, split our party and with likely nothing to show for it", the letter said.
Education Minister Damian Hinds said the European elections were in effect a second referendum and would be hard for the Conservatives.
But the prime minister's official spokesman said the government believed it was "imperative" that the Withdrawal Agreement Bill - the legislation required to leave the European Union - was brought to Parliament in time for it pass all its stages by the summer recess.
Opinion polls are broadly finding voters are turning against the two main parties and toward smaller parties that either back leaving the European Union or want to remain in the bloc.
'And this is where in my judgement we are going to have to come to an accommodation with the Brexit Party.
Labour's Brexit pointman, Keir Starmer, told The Guardian newspaper that any cross-party deal lacking a confirmatory referendum would not pass parliament as about 150 Labour lawmakers would oppose such a deal.
Two parties which support staying in the European Union, the Liberal Democrats and the Greens, were on 15 per cent and 11 per cent respectively.More news: Hotel Guests Found Dead, Impaled by Crossbow Bolts
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"By contrast where does a supporter of Brexit who doesn't like Nigel Farage go?", he asks, adding a warning that while the "Remain" parties could do well in terms of share, the splintered nature of the vote could hit the number of seats gained (because of threshold that parties must cross). "We have been betrayed not just by the Conservatives; Labour has done the same thing too".
The new deadline for leaving the European Union is October 31 though many Brexit supporters fear that the whole divorce could be derailed. Its chair, Graham Brady, has urged her to set out a clearer timetable for her departure if her Brexit deal is not passed.
On May 23, British citizens and European and Commonwealth citizens resident in the United Kingdom will vote to select 73 candidates for the European Parliament, who will take up their seats in July for a five-year term.
Labour, which is running second in the polls, is also being tested by the elections.
He insisted Remainers will back The Brexit Party, saying: "Oh, they will".
Two senior Labour frontbenchers have thrown their weight behind calls for a second referendum on a cross-party Brexit deal to gain the backing of their MPs.
Labour is proposing Britain remaining in a customs union with the EU, a position that's anathema to the hardline Brexiters, nicknamed the "Spartans", in May's party, but doesn't go far enough to satisfy the almost three out of four Labour Party members who are pro-EU.
At a stormy meeting on Monday of the Parliamentary Labour Party (PLP), Wes Streeting, a critic of Mr Corbyn, warned that he would lead them to electoral defeat and was "a bigger issue for us than Brexit".
While the poll found that the Brexit Party would hammer the Conservatives, it forecasted that Jeremy Corbyn's Labour Party would win a general election, taking about 27% of the vote.