The government’s proposed pupil premium could target more than a quarter of the poorest children, Nick Clegg said this week.

The Deputy Prime Minister made the claim while giving a speech on social mobility in a west London children’s centre organised by think-tank Centre Forum.

The pupil premium, additional funding that will be attached to students from the lowest household incomes, is one of the Liberal Democrats’ key policies to be adopted by the Conservatives.

The Lib Dem leader said the premium would affect between 15 and 26 per cent of the country’s poorest pupils once a decision was made on what the criteria would be to allocate the money, such as free school meal eligibility or tax credit indicators.

He said the level of the premium would be announced in October’s spending review, but according to the Department for Education’s impact document, the amount would be made public in November.

Before the election, the Lib Dems had pledged to give #163;2.5 billion to less well-off pupils, but the Coalition agreement released in May merely stated that a “significant amount” would be provided.

Speaking on Wednesday, Mr Clegg said: “In five years’ time we want to be able say that the children born in 2015 are less constrained by the circumstances of their birth.”

Mr Clegg is “holding the fort” for Prime Minister David Cameron while he is on holiday. He also confirmed that former Labour health secretary Alan Milburn has been appointed the Government’s independent reviewer on social mobility.