LABOUR'S Falkirk row has taken a dramatic twist with the party leadership referring the allegations of ballot-rigging by Unite, Labour's biggest donor, to the police.

A senior party source insisted the referral was unrelated to a move by Tory backbencher Henry Smith, who has written to Police Scotland Chief Constable Sir Stephen House, asking for a police investigation.

The Labour source said the party leadership had acted swiftly and thoroughly throughout.

It is believed Labour's referral is based on allegations that trade unionists were signed up as local members in Falkirk without their prior consent and that there was unauthorised use of personal data.

The referral to the Scottish authorities came as the public war of words between Mr Miliband and general secretary of the Unite union, Len McCluskey, continued.

The Labour leader said: "Instead of defending what happened in Falkirk, Len McCluskey should be facing up to his responsibilities.

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

The union chief hit back, saying: "It's depressing Labour leaders seem to want to have a Clause Four moment, where they front up union leaders. Ed doesn't have to front up me – I'm his friend, I support him."

But Mr McCluskey said it was nonsensical for Mr Miliband to be "hooked into this hysteria because the media and the Tories want to demonstrate a division".

Lawyers representing Unite said the union does not "participate in unlawful activity or in activity that is anything other than democratic or transparent".

Meantime, Conservative HQ suggested the Labour leader had panicked and had been bounced into calling in the Scottish authorities after Crawley MP Mr Smith asked for a police probe.

It said it was handing over to police a Unite document it had obtained, listing 41 constituencies in which the union had supported candidates for selection.

A Police Scotland spokesman said: "We can confirm we are in receipt of this correspondence and it is currently being considered."

Mr Miliband's aides insisted the move is part of a determined bid to assert his authority within the Labour movement and show that he will not be "pushed around" by Unite.

His move is a high-stakes gamble given the trade union is Labour's biggest donor – donating £11 million since 2007 – with around 80 MPs sponsored by Unite at Westminster.

It is claimed Unite recruited more than 100 members to Falkirk Constituency Labour Party (CLP) in a bid to have Karie Murphy, a former Unite officer who works for Tom Watson MP, selected.

It denies any wrongdoing and insists all it was trying to do was to recruit more members to Labour.

It is believed the referral is over allegations that some trade unionists were enlisted to Falkirk CLP without their consent and that their personal details were not authorised.

In May, the CLP selection was halted amid complaints of Unite ballot-rigging.

The following month an internal inquiry was completed, the CLP candidate selection was immediately put under "special measures" – central control – and Iain McNicol, Labour's general secretary, was asked to review membership procedures.

Then, following the review, Ms Murphy and Stephen Deans, Chairman of Falkirk CLP and Unite in Scotland, were suspended.

Following legal advice the Falkirk selection report was referred to the procurator-fiscal on July 5.

On Thursday, Labour's election chief Mr Watson quit, and yesterday Mr Miliband took to the airwaves to attack Mr McCluskey.

Mr McCluskey branded Labour's handling of the Falkirk row disgraceful and absolutely amateurish.

Prime Minister David Cameron, meanwhile, sought to continue piling the pressure on his Labour opposite number, claimed Mr Miliband had lost control of his party.