David Cameron has said the government is still committed to abolishing the 50p top rate of tax, despite a report suggesting that it raised significant extra funds in its first year.

The tax, introduced by Gordon Brown in 2010, has been a source of tension within the coalition. Conservatives are eager for the 50p rate to be scrapped but the Liberal Democrats are insistent that it should not be abolished just to benefit the rich.

A report by HM Revenue & Customs (HMRC) is expected to show a "surge" in revenues in its first year totalling hundreds of millions of pounds, according to the Daily Telegraph, which reported that the government had decided to put off scrapping the tax until at least 2015.

Speaking to Sky News's Boulton & Co, the prime minister acknowledged that the government had to "demonstrate fairness" when making the decision, but made plain where his sympathies lie.

"It is temporary; we don't want high marginal rates of tax," he said. "We have also got to look at the evidence of the 50p tax. Is it raising a lot of revenue? If it isn't then clearly there will be question marks over it."

The HMRC report was commissioned by George Osborne last year to assess how much revenue the change in the top rate had raised. The chancellor has made little secret of his opposition to the rate, which applies to incomes over £150,000.

Tensions between the coalition partners escalated over the issue after a letter was published in the Financial Times from a group of economists saying the 50p rate should be abolished "at the earliest opportunity" to boost growth.

The energy and climate change secretary, Chris Huhne, responded by warning Osborne to "forget" any change to the 50p rate if the move was designed to help the Tories' "friends" in the City.

The deputy prime minister, Nick Clegg, promised to keep the rate as it stands, although he said he would back abolition in the long run if it was not raising much revenue and if it was replaced by new taxes on "unearned income".

One of the alternatives suggested by the Lib Dems is a "mansion tax" on high-value properties.