DAVID Cameron has sought to exploit Labour's troubles in Falkirk by claiming Ed Miliband is a weak leader who takes his orders from the leader of the Unite union, the party's biggest donor.

Amid some of their sharpest exchanges yet at Prime Minister's Questions, Mr Cameron used every opportunity he could to taunt Mr Miliband about his relationship with Unite general secretary Len McCluskey, accusing him of being "too weak to stand up to the Unite union, too weak to run Labour and certainly too weak to run the country".

The Labour leader accused the Prime Minister of peddling double standards on ethics, pointing to Mr Cameron's "dinners for donors" and the "tax cut for his Christmas-card list".

Mr McCluskey declared his full support for Ed Miliband as Labour revealed that, across the UK, up to 500 of his members have had their party subscriptions paid for by trade unions.

He made his comments as the practice is being scrutinised by Iain McNicol, Labour's general secretary.

Unite is facing allegations it sought to fill Falkirk Constituency Labour Party (CLP) with its own members to ensure its preferred can- didate, Carie Murphy, won the selection process to be the local CLP's next General Election candidate.

While the union insists it has done nothing wrong, it is thought it was able to recruit more than 100 new members to Falkirk CLP, which originally only had 200 members.

Tory HQ has called on the Information Commissioner to investigate whether a breach of the Data Protection Act has taken place because of claims at least one trade unionist was enrolled as a Labour member in Falkirk without his consent.

Amid bitter exchanges at PMQs, Mr Cameron claimed Mr Miliband, was in thrall to Mr McCluskey, who, he said, now controlled Labour.

Brandishing a sheet of paper which the PM said detailed Unite's plans for "a firmly class-based and left-wing General Election cam-paign", he told Mr Miliband: "You are taking your script from the trade unions, who don't like choice - and they want to control everything.

"What we know is one organisation they have got control of, we see it in black and white; they have taken control of the Labour Party."

However, the Labour leader hit back, accusing the PM of hypocrisy, saying he would take no lessons from the man responsible for "dinners for donors".

A senior Labour source stressed how when Labour found concerns in the selection process at Falkirk it acted swiftly and thoroughly.

He confirmed there were 14 other CLPs under so-called "special measures", that is, central control but most went back to before 2005.

Asked about Mr Miliband's personal relationship with Mr McCluskey, he said: "We have a lot of respect for Unite. Unions are a good thing. We believe in the union link. There's a determination over the issue in Falkirk. That's not affecting their personal relationship in any way."

However, the source insisted the party would not bow to Mr McCluskey's demand to halt the Falkirk selection, saying it would go ahead and take four to six weeks to complete.

Mr McCluskey rallied behind the Labour leader. He accused Mr Cameron of cheapening the office of Prime Minister with his petty political point-scoring and of showing a shameful lack of concern about the real issues besetting Britain.

Falkirk MP Eric Joyce said Unite's leadership had behaved abominably and really damaged the game for everyone.

He added: "There can be absolutely no question about who runs the Labour Party: it is Ed Miliband and he has my full support."