Media playback is unsupported on your device Media caption Listen to Boris Johnson on Nick Clegg's weekly radio phone-in for LBC 97.3

London Mayor Boris Johnson has demanded that Deputy Prime Minister Nick Clegg gets ministers out of their "posh limos" and onto public transport.

Mr Johnson was posing as "Boris from Islington" on the Lib Dem leader's weekly radio phone-in for LBC 97.3.

In a pre-recorded message, the Mayor said the government needed to spend more on London's transport system.

Mr Clegg insisted the coalition had "slashed" the ministerial car budget.

The Liberal Democrat leader was answering callers' questions on his weekly phone-in, when he was played the message from Mr Johnson.

'My challenge to Boris'

He said: "Hi Nick, it's Boris from Islington. When are you going to get all those government ministers out of their posh limos and onto public transport like everybody else?

"And how can we possibly expect government to vote for increases in infrastructure spending which we need in this city, and upgrading the Tube which we all need, when they sit in their chauffeur-driven limousines paid for by the taxpayer?"

He signed off with the message: "Nick - get them out of their limos. Boris, over and out."

When Mr Clegg was told that the question had been recorded before the show and Mr Johnson was not on the line, he joked: "Well that's easy for him, isn't it?"

He said the government had cut the ministerial car bill inherited by the previous Labour government "I think by about 70%", which he described as "a big step in the right direction".

He said ministers did not use cars all the time, adding that he was travelling to Sheffield later by train.

Mr Clegg agreed with Mr Johnson on the need for infrastructure spending, "which creates jobs today... and helps the economy in the future".

He said Chancellor George Osborne had offered £50bn of Treasury guarantees for spending on infrastructure projects.

"So my challenge to Boris is," he said, "is he going to use these guarantees to help Londoners?"

Talk show host Nick Ferrari revealed the Mayor would be on his show the following week, to which Mr Clegg said: "Tell him to get out of his limo and get the infrastructure projects that we're offering, moving."

On the BBC's Daily Politics programme, Plaid Cymru leader Leanne Wood was asked about reports the Welsh Secretary used his ministerial car "to travel 110 yards from his office to Downing Street".

Ms Wood said most people would have difficulty "understanding the rationale" behind such perks when "so many ... are struggling to make ends meet".

She said there may be an argument for having a driver to go to certain meetings, but not for such short distances.

"Everyone else has to manage [on public transport]", she told the programme.