Image copyright PA Image caption UKIP, led by Nigel Farage, came second to Labour by a margin of more than 10,000 votes

UKIP is "reviewing the evidence" before deciding whether to make a formal complaint about what it suggests may have been electoral fraud in the Oldham West and Royton by-election.

Leader Nigel Farage has claimed people with "bundles of postal votes" had turned up at polling stations and some wards had voted exclusively for Labour.

But Labour-run Oldham Council said it had not received any complaints.

It said it had "robust systems" in place to identify electoral abuses.

And Labour's deputy leader Tom Watson said the allegations sounded like "sour grapes" from its opponents.

Prior to the by-election, there had been suggestions that UKIP could run Labour close but, in the event, Labour candidate Jim McMahon romped to victory with a 62% share of the vote, polling 10,722 more votes than his closest rival.

'Very odd'

Media playback is unsupported on your device Media caption Farage: ‘Electoral process dead’ in Oldham

Speaking in the wake of the defeat, Mr Farage told the BBC that "we will file a formal complaint against the abuses that our people saw yesterday".

He said Oldham's Asian population had voted for Labour in large numbers, even though, he claimed, some did not speak English but were signed up for postal votes.

He claimed to have seen ballot boxes in which "99% of the votes were for Labour" and "this does not seem to be consistent with modern liberal democracy".

"Some very odd things happened," he told BBC Radio 4's Today. "There was a 15% increase in the number of postal votes yesterday and stories of practices that should not be happening in a modern democracy."

"Some of the things we've seen before in Birmingham and Tower Hamlets I have reason to believe were happening in Oldham yesterday".

Media playback is unsupported on your device Media caption Watson: Farage complaint 'sour grapes'

Some of those who voted for Labour, he suggested, had not heard of UKIP, the Conservatives "or even Jeremy Corbyn" and while acknowledging this would not have changed the result, he said Labour would have had a "massively reduced" majority.

He claimed Labour was at an advantage because it ran the local council and therefore "controlled council housing, social services and deep and very strong links with the mosques and other Churches".

He added: "It means that in some of these seats where people don't speak English but they are signed up for postal votes effectively the electoral process is now dead".

'Robust system'

However, two hours later UKIP backtracked slightly and said it would consider the evidence before lodging an official complaint.

Mr Watson said that UKIP - who claimed beforehand that the election was a referendum on Jeremy Corbyn's leadership - were "crying over spilt milk".

"It seems like sour grapes to me. If he has got evidence of that, he should have told the police immediately. I have talked to my organisers and they have got no knowledge of that. If you look at the scale of the result it was pretty decisive."

And Oldham Council said there had been a "high level of daily scrutiny" of the by-election, the first to be run under the new system of individual electoral registration - where people have to sign up to vote themselves rather than being registered as a member of a household.

"We have a robust system in place for adjudicating postal votes which includes comparing the signatures and dates of birth in the submitted postal vote application to those within the postal vote statements," it said.

"Where those do not match, the postal vote is rejected and not included in the count.

"We take our duties in administering the voting and count process very seriously and if we receive any allegations of postal voting irregularities then we would be immediately reported these to the police so they can be fully investigated.

'Integrity concerns'

The Metropolitan Police is investigating 16 allegations of electoral malpractice in relation to this year's mayoral election in Tower Hamlets, relating to voter of registration and the improper distribution of election literature in the east London borough.

The election was re-run after incumbent Lutfur Rahman was convicted of electoral fraud during the 2014 poll and removed from office.

Conservative MP Stuart Jackson said he shared Mr Farage's concerns about "postal voting on demand" and would be raising the issue of the "integrity" of postal voting in a debate in Parliament next week.

He tweeted: "Timing unfortunate but Farage is right on "community" postal voting. Time to scrap postal votes on demand."

In a report earlier this year, the Electoral Commission named Oldham West and Royton as one of the constituencies alleged to have a "greater risk" of voter fraud.

The watchdog has said the move to IER will further reduce the risk of fraud but said it would not rule out seeking a change in the law to make it an offence for campaigners to handle any postal voting materials.