Brexit frustrations make snap election a big gamble for Johnson

* Brexit supporters frustrated by failure to leave EU

* Johnson wants early election to strengthen mandate

* Conservatives face losing some voters to Brexit Party

* Brexit Party seeks "non-aggression pact" for election

By Andrew MacAskill

LINCOLN, England, Sept 13 (Reuters) - James Bowkett is a long-time Conservative Party supporter who voted in 2016 for Britain to leave the European Union.

Three years later, the 58-year-old businessman is fed up waiting for Brexit to happen and is considering abandoning the Conservatives in a looming snap election.

"I am giving up on the Conservatives. There are too many people in that party who don't want to listen to the public," Bowkett, 58, said holding up an umbrella on a rainy day this week in Lincoln in eastern central England.

"I am beginning to doubt that Brexit will happen, and I don't think the Conservatives can deliver it alone."

Bowkett is just the sort of voter Prime Minister Boris Johnson needs if he is to win an election following parliament's rejection of a Brexit deal agreed by his predecessor, Theresa May, and the EU's refusal to renegotiate it.

Johnson wants an election to strengthen his mandate for pulling Britain out of the EU after his Conservative government lost its majority over his handling of Brexit. Opponents refuse to endorse an early election unless he rules out leaving the EU without a deal, which could cause a disorderly Brexit, but a snap poll is likely sooner or later.

It is a risky move. If Johnson fails to carry out a pledge to leave the EU on Oct. 31, frustrated Brexit supporters like Bowkett could be driven into the arms of the Brexit Party founded this year by eurosceptic Nigel Farage, polls show.

Johnson could lose power, the main opposition Labour Party could enter government and Brexit might never happen.

Even if Johnson can persuade the EU to accept a revision of the deal reached by Theresa May, it is unlikely to be enough to appease voters like Bowkett.

"If that (revision) happens, all this fighting will have been pointless," Bowkett said. "We will be the laughing stock of the world."

ELECTION GAMBLE

To win a majority in a general election, Johnson will be banking on winning in places such as Lincoln, a cathedral city that was an important settlement in Roman times and lies 120 miles (193 km) north of London.

The constituency, narrowly held by Labour, has been a bellwether of national trends in all but one election since 1979.

It voted 57% in favour of quitting the EU in the 2016 Brexit referendum - compared to the nationwide margin of 52-48 - and the Brexit Party finished top in local voting in European elections in May, as it did in the national vote.