UKIP confusion as party backtracks on Farage's claims that Oldham by-election was FIXED
But just minutes later a senior UKIP insider revealed to Express.co.uk that one of Mr Farage's tweets – believed to be the second where he said the result had been rigged – had "overstepped the mark".

The source said: "I understand that there was one tweet that may have overstepped the mark, I think some wrong information was given.

"But there's no doubt – I've never seen in 25 years of being involved in politics where you get over 15 per cent of the total votes run in on the last day. That is very weird."

It is thought that Mr Farage will address the issue during an interview tomorrow morning.

The insider added: "The questions about postal voting have been going on for a long time.

"Nobody is suggesting there's been fraud here. We are not formally suggesting there has been any fraud, Labour has been very efficient.

"We deal with it, but we feel there should be reform and there have been plenty of cases. It's just odd.

"The system is as it is, the Labour Party is a machine that's very effectively using it. Good on them. But they've won anyhow, so let's not get too het up on that."

And a defiant Labour source told Express.co.uk: "We totally reject that claim. Mr Farage doesn't seem to have any evidence to support his claim.

"We won the election in every community in the constituency with both postal voters and non-postal voters.

"If Ukip makes claims, they should demonstrate evidence to back it up."