David Cameron defends the government's planned changes to benefits insisting welfare reforms are fundamentally fair - and sets his sights on being prime minister until 2020.

Child benefit cuts here to stay - Cameron (R)

The coalition has come under increasing criticism for its proposed changes to child benefits, including the decision to reduce child benefit for families where one parent earns more than £50,000. The government is also proposing that most working age benefits be limited to a 1 per cent rise - a move that will be voted on in the Commons on Tuesday.

But the prime minister on Sunday insisted the move was the right approach. In an interview with the Sunday Telegraph, he urged critics within his own party to stop complaining about the coalition, and stood behind the welfare reforms being pushed through.

He said the changes to child benefits would affect the top 15 per cent of earners, and added: "Look, I have complete understanding for people who are having their family budgets changed and money taken away and if there is more we can do to make it easier for people, yes of course."

He later told the BBC: "I'm not saying those people are rich but I think it is right that they make a contribution.

"This will raise £2bn a year. If we don't raise that £2bn from that group of people, the better off 15 per cent in the country, we would have to find someone else to take it from."

Read more: How will my benefits change?

Mr Cameron's comments come a day before the coalition publishes a mid-term review, detailing the progress made since the rose garden moment in 2010 and setting out its top priorities for the rest of their term. It is expected to include future policies on pensions and transport, as well as details of a cap on social care costs, which ministers have considered setting at £75,000, as well as pension and child care reforms.

"This is an enormous reform agenda and that's enough to keep us all busy," he told the Sunday Telegraph, adding that he wants to serve as prime minister until 2020.

The prime minister also warned Tory critics of the power-sharing government to "stop complaining" and insisted he would not turn back on same-sex marriage, child benefit cuts for the wealthiest and overseas aid commitments.