Ukip was today facing claims it had covered up a poll indicating leader Nigel Farage could face defeat in South Thanet.

The result of the poll showed Farage had fallen behind his Tory opponent Craig Mackinlay.

The results were leaked to the Mail on Sunday, which published them today in a story claiming the Ukip leader faced a 'humiliating defeat.'

Farage has vowed to resign if he fails to win South Thanet.

The ComRes poll of 1,003 people was commissioned last month by businessman and former Tory Arron Banks, the Mail on Sunday reported.

It puts Mackinlay on 31%, Farage on 30% and Labour's Will Scobie on 29%.

A Ukip spokesman told the Mail on Sunday the results were 'unreliable' and that it was a 'rogue poll'.

Speaking of the importance of winning South Thanet, Farage has previously said: "It is frankly just not credible for me to continue to lead the party without a Westminster seat of my own.

"What credibility would Ukip have in the Commons if others had to enunciate party policy in Parliament and the party leader was only allowed in as a guest?

"Am I supposed to brief Ukip policy from the Westminster Arms pub? No – if I fail to win South Thanet, it is curtains for me. I will have to step down."

Craig Mackinlay said today: "This is another terrible indictment of Ukip's honesty and integrity.

"Only two weeks ago they had to kick out Janice Atkinson MEP over her expenses. now they have been caught out trying to suppress the findings of a poll because they didn't like the result.

"Nigel Farage is an absentee candidate who is seldom seen in the constituency and is merely using it as a launching pad for himself, but that is no excuse for trying to pull the wool over the eyes of voters."

He added: "The race between the Conservatives and Ukip in South Thanet is a tight one. I will be fighting all the way for local people and will always put their interests first."

Yesterday, Labour candidate Will Scobie urged people to vote tactically to stop Farage becoming MP for South Thanet.

In a letter to constituents, he said: ""If previously you have voted Conservative or Liberal Democrat, I ask you to lend me your support and join Labour voters, even for this election only, so we can vote to save South Thanet and defeat Nigel Farage."

He said today: "Labour is fighting for every vote in South Thanet. We are out every single day talking to hundreds of voters about the issues. What is clear is that a vote for any party other than Labour will lead to more privatisation of the NHS. I have lived in South Thanet my entire life and I am fighting to improve the area and protect the local hospital I was born at."

However, our political editor Paul Francis said today's poll would mean Scobie's plea may not gain much traction from Conservative supporters.