Media playback is unsupported on your device Media caption Labour leader Ed Miliband: ''At all times, we have acted to uphold the integrity of my party''

Ed Miliband is refusing to back down in his fight with Labour's biggest union backer over its influence in the party.

The Labour leader has asked police to look at alleged irregularities in a candidate selection race in Falkirk.

According to an internal Labour report, Unite members were being signed up to the local party without their knowledge in a bid to rig the contest.

Unite leader Len McCluskey said his union had done nothing wrong and he was disappointed at the turn of events.

Labour HQ has taken over the selection contest in Falkirk but has not said why it has involved the police.

Mr McCluskey denies claims Unite tried to fix the contest to get its preferred candidate selected and claims the internal Labour is a "stitch up" designed to smear the union.

'Bad practice'

Mr Miliband has dismissed the smear claims as "total nonsense" and said that, instead of defending these practices, Mr McCluskey should be "facing up to what happened in Falkirk".

Analysis There are a million questions still to be clarified about what exactly went on in Falkirk, but there is no doubt that in sending their evidence to the police, Ed Miliband and Labour have chosen to escalate this row with Unite to a stratospheric level. Now it may be that he had little choice with political opponents taking similar steps, nevertheless many in the unions will see this as akin to turning in a family member. Nothing may come of it. There may be nothing to find. But if you were thinking that this was all shadow boxing up till now, think again. It has without doubt become the biggest test of the Labour leader's time in charge, and could define the party's future relationship with the whole union movement. Who will blink first?

"The Labour Party I lead will select its candidates in a fair and transparent way. We will act without fear or favour," said Mr Miliband.

"He should not be defending the machine politics involving bad practice and malpractice that went on there. He should be facing up to it."

Mr Miliband said the party's inquiry had shown "people were being signed up as members of the Labour Party without their knowledge. It says that bad practices were going on. It says people were being asked to sign up to the Labour Party on the condition that they supported particular candidates.

"We are not having this in the Labour Party."

Labour's shadow business secretary Chuka Umunna told the BBC: "We took advice yesterday in relation to the Falkirk matter and as a result of the advice given, have decided swiftly and strongly to refer it to the police."

It is not clear why the party considers it might be a police matter. Mr Umunna told the BBC he could not comment about why as legal advice was "subject to prejudice".

The Conservative MP Henry Smith had also written to the Chief Constable of Scotland, Sir Stephen House, asking for an inquiry and suggesting Unite might have committed fraud.

Mr McCluskey told reporters he was "clearly disappointed at the developments back in London" adding: "It seems to me that the Labour leadership has now been caught up in anti-union Tory hysteria and I'm amazed as everyone else is at this."

'Done nothing wrong'

He said he supported Ed Miliband as Labour leader but said: "We are in the middle of a media storm which is being caused by Labour's inability to deal with this situation."

He said he would co-operate with any police inquiry but wanted an independent inquiry that would be made public: "As far as Unite's concerned we have done nothing wrong."

Media playback is unsupported on your device Media caption Len McCluskey: "The way its been handled by the Labour Party headquarters is nothing short of disgraceful"

The Conservatives said Mr Miliband should have acted sooner.

A spokesman said: "This is followship, not leadership, from Ed Miliband. Why didn't he refer Falkirk to the police days ago?"

He added: "Will Ed Miliband now come clean, and admit that this scandal goes wider than just Falkirk?

"Unite have already admitted that they are targeting another 40 Labour selections, as Len McCluskey continues to take over the Labour Party."

But Mr Miliband told BBC political editor Nick Robinson the party had acted "thoroughly and decisively" since allegations were first raised in May, first suspending the selection process, then holding its own inquiry and then referring the matter to the police.

He also rejected Mr McCluskey's suggestion that he was seeking his own "Clause IV moment" - a "situation where [Labour leaders] punch up union leaders" - saying he was acting "to uphold the integrity of my party".

The party has already stepped in to run the selection process in Falkirk centrally, and has suspended the rules under which unions could sign up members to Labour and pay the fees on their behalf.

On Thursday, Labour's general election co-ordinator Tom Watson, whose office manager Karie Murphy was Unite's preferred candidate in Falkirk, quit for the "future unity" of the party.

Mr Watson told BBC Radio WM that he had been thinking about it for a few months but the "fuss" about the Falkirk selection had persuaded him it was time to move on.

But he added: "I think David Cameron's portrayal of the situation, that everyone is in hock to Len McCluskey, is just not true."

Falkirk selection row: Who's who?

Image copyright AFP Image caption Ed Miliband: In 2011, the Labour leader made Tom Watson deputy chairman of the Labour Party and 2015 general election co-ordinator, to oversee the selection of Labour parliamentary candidates.

Image copyright Getty Images Image caption Tom Watson MP: The former union official resigned as election co-ordinator over the Falkirk selection inquiry. He told Mr Miliband he was also tired of the shadow cabinet "merry-go-round". He has close ties to Unite's Len McCluskey.

Image copyright PA Image caption Karie Murphy: Tom Watson's office manager and Unite's preferred candidate for Falkirk. She has been suspended by the party along with Falkirk party chairman Stephen Deans.