Nick Clegg is set to reveal a £50m plan for summer schools to help needy students from "going off the rails"

He will also claim the unions have bought the Labour Party and will challenge Ed Miliband to support radical reform of political party funding.

In a speech to his party's conference in Birmingham on Wednesday, the Liberal Democrat leader will urge Miliband to accept proposals that would cap the amount of money individuals and organisations are allowed to donate.

"Of all the claims Ed Miliband has made the most risible is that his party is the enemy of vested interests. Today Labour is in hock to the trade union barons - after their government stipend, 95 per cent of Labour’s money comes from unions. Most of it from just four of them," he will say.

"Let me be clear: the values of trade unionism are as relevant as ever. Supporting workers. Fighting for fairness at work. But I don’t think the unions should be able to buy themselves a political party."

Next month the independent Committee on Standards in Public Life is expected to recommend a £10,000 cap on donations to political parties, compensated for with an increase in public funding.

The plan was prompted by a survey conducted by the committee which found much of the public believed politicians "very often" do special favours for people and organisations who give large donations.

Aware of criticisms that he is too close to the unions, Miliband is due to shake-up the rules governing Labour's leadership elections.

The move would give people who are not members of either the Labour Party or its affiliated unions a say in the choice of future leaders.

Miliband himself secured the leadership largely as a result of support from the unions and has been keen to distance himself from the "Red Ed" label. His rough treatment at the hands of union members at the TUC conference last week would not have been entirely unwelcome.

But he has to tread a careful line as the party is heavily reliant on union funding with the latest figures showing of the £3.2m it received, £2.65m came from unions.

A donation cap would also hit the Conservative Party, who have been conversely criticised for taking too much money from wealthy individuals in the City.

Research conducted by the Bureau of Investigative Journalism showed that 57 individuals from the financial services sector made a donation to the party of more than £50,000 each in 2010. And since 2005, ten individuals alone have given more than £13m.

In his speech Clegg will also attempt to paint the Lib Dems as free from the stain of Rupert Murdoch. He will tell his activists that they should be proud to "have never served the media moguls" the "union barons" or the bankers.

"We are in nobody’s pocket. That’s why we speak up, first and loudest, when the establishment lets the people down," he will say.

In the wake of the phone-hacking scandal the Lib Dems have largely avoided the embarrassment of having had close ties to News International. Although detractors argue that is because Murdoch did not consider Britain's third party worth bothering with.