London mayor Boris Johnson has repeated his call for the tax rate to be cut to 40p - and declined to rule out the possibility of it happening before the general election.
Earlier, the Liberal Democrat Chief Secretary to the Treasury - Danny Alexander - said the rate would be cut "over my dead body".
"The last thing I want to see is a pointless sacrifice from the Liberal Democrats, let alone the dead body of Danny Alexander," he told BBC Radio 4's Today programme.
"Sooner or later there will have to be a new Conservative manifesto and I can't believe we are going to go into an election on a campaign to keep our tax rates higher."
Asked if that meant he accepted it could not happen until after 2015, he said: "Who can say what will happen to Danny Alexander? Stranger things have happened at sea."I don't think that it is reasonable always to keep UK tax rates higher than those of competitor countries.
"UK income tax is now higher than the average in the EU. That never used to be the case. I don't see why it should be the case for the long term and I see no reason why we shouldn't bring it down."
Chief Secretary to the Treasury Danny Alexander said the Liberal Democrats would not allow a cut to the top rate of tax in this Parliament.
In an interview with the Daily Mirror, he was asked about David Cameron's refusal to rule out cutting the top rate and replied: "You'll have to ask them (the Tories) why they answer those questions in those ways.
"If you ask me would I cut the top rate below 45p the answer is 'no'. In this Parliament we will not allow that to happen."
Mr Alexander also had some praise for Labour's Ed Balls - amid questions over whether the Lib Dems could work with the party in a future coalition.
"I play cricket with Ed Balls. I have opened the bowling at Lords while he kept wicket behind the stumps and I have to say he didn't let anything past him. So I would endorse him as a wicket keeper," he said.