Ed Miliband has pledged to put an end to the "scandal" of long-term unpaid internships that keep the poorest young people from the best careers by banning placements that last for more than four weeks.

The Labour leader claimed the system is rigged in favour of wealthy families that can afford to support their children while they work for free for months on end to get a foot in the door in fiercely competitive fields such as law, finance and the media.

Launching Labour's manifesto for young people, Mr Miliband said companies will be forced to pay interns at least the minimum wage if they keep them on for more than one month if he takes the keys to No 10 next month.

In a speech to students at Bishop Grosseteste University in Lincoln, he said: "In this country, if you want a good job in a sought after sector, you're often asked to work for free, month after month after month.

"That puts careers in highly prized jobs - in the arts, media, fashion, finance and law - out of reach for huge numbers of highly able young people.

"It's not fair. It's not right. And it prevents our companies drawing on all the talents our nation has to offer.

"So we'll put a stop to it."

"It's time to end a system that's rigged in favour of those who can afford it," he added.

It's time to end the scandal of unpaid internships in our country."

Educational charity the Sutton Trust estimates there are around 22,000 unpaid interns in the UK at any one time and around 31% of graduates on placements are not being paid.

Work experience can cost more than £900 a month in London and nearly £800 in Manchester before transport costs are even factored in, according to Labour.

The party pointed to YouGov polling released by campaign group Intern Aware which found that a four week legal limit would not lead to a reduction in internships, with 62% of businesses saying it would make no difference to how many placements they ran.

Labour has long said it would look at reforms but has also suffered its own embarrassments over the practice, including in 2011 when Lyn Brown, Labour MP for West Ham at the time, was accused of hypocrisy after advertising for an unpaid worker in her office despite campaigning for a ''living wage for all''.

The party's mini-manifesto also set out its pledge to cut tuition fees from £9,000 a year to £6,000 while also increasing maintenance grants by £400.

Mr Miliband told the students that Nick Clegg's decision after the last election to u-turn on tuition fees had "damaged everyone in politics" and insisted he would keep his pledge.

He said: "Five years ago Nick Clegg made a promise on tuition fees and he broke it.

"Four years ago, I said I wanted to cut tuition fees to £6,000."

"I am going to keep my promise," he added.

Plans to guarantee high quality apprenticeships for all school-leavers that achieve the necessary grades and ensure paid starter jobs with training for young people unemployed for more than a year were outlined in the mini-manifesto.

Labour's plans to giving 16 and 17 year-olds the right to vote also featured.