-It marks a steep 22 per cent rise from Gordon Brown's leadership
-Tories claim Ed Miliband is even further in thrall to union barons
-Largest donor is Unite with £7.5 million given over two years
Labour has banked more than £20million in funding from unions since Ed Miliband became leader.
The money accounts for 81 per cent of donations to the party over the past two years.
It marks a steep rise from Gordon Brown's leadership, when unions provided 59 per cent of donations to the party.
Tory critics claim this shows Mr Miliband is even further in thrall to union barons than was his predecessor.
Union votes were vital in securing Mr Miliband's victory against his brother David in the 2010 party leadership election.
Figures released by the Electoral Commission show that the largest single donor was Unite, led by militant firebrand Len McCluskey. The union gave £7.5million over the two-year period.
Mr McCluskey suggested last year that he expected donations to influence policy, saying: 'I've got no intentions of bailing out the Labour Party with money until such times that they start to represent the views of ordinary working people.'
The party also received £3.6million from the GMB and the same amount from Unison. Mr Miliband has come in for criticism for his relationship with the unions.
In October he spoke at the TUC's anti-cuts march in central London, where some of those in the 150,000-strong crowd carried placards calling for a '24 hour general strike'.
The TUC had voted to consider a general strike for the first time since 1926 to oppose Coalition spending cuts.
Iron grip: Tory chairman Grant Shapps said Mr Miliband's reliance on his 'union paymasters' is clearer than ever
The figures show Labour has received total donations excluding public funds of £25million since Mr Miliband was elected.
Mr Brown's Labour received £59million in his three years as leader, of which nearly £35million came from trade unions.
Conservative Party chairman Grant Shapps said: 'Miliband's reliance on his union paymasters is clearer than ever.
'These figures underline the iron grip union barons have on Miliband.'
But Labour have accused the Tories of giving rich donors too much influence over policy.
In the summer, official figures revealed that £790,948 was donated to the Tory Party by just eight individuals.
Another £710,000 came from donors attending 'Leader's Group meals' with Mr Cameron and other senior figures such as Home Secretary Theresa May and Communities Secretary Eric Pickles.
Large sums have also been given to the Tories by hedge fund boss George Robinson, who was ordered to pay back £2million in tax after a judge ruled against an offshore scheme.
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