Liberal Democrat leader Nick Clegg has backed road pricing in the West Midlands.
In an interview in The Birmingham Post, he said he backed road pricing in all of Britain's big cities.
But he warned charging drivers was politically impossible unless the Government provided funding for public transport.
Birmingham's Conservative and Liberal Democrat-controlled council has ruled out joining the first wave of local authorities out-side London to introduce congestion charging. Councils in Greater Manchester have applied to introduce it.
Ministers have been criticised for failing to give a guarantee extra cash to improve public transport services will be available to regions imposing charges.
Birmingham and neighbouring authorities have said they will continue to review the options and may apply to introduce road pricing.
Criticising the Government's current approach, he said: "It's the Government saying we don't have the guts to pilot these schemes on national trunk roads and motorways, so we are going to pass the buck to local communities to use the public as guinea pigs."
Mr Clegg also defended a Liberal Democrat MP who shocked colleagues by describing a Minister as "an arsehole" in a Commons debate.
Leeds MP Greg Mulholland used the word to refer to Health Minister Ivan Lewis during a debate in Westminster Hall.
He was angry Mr Lewis had criticised Liberal Democrat policy towards hospices then refused to let him reply.
Mr Clegg said: "Of course it's not appropriate for him to call someone an arsehole, and Greg has apologised, or has said he recognises that is not customary parliamentary language.
"But Greg feels very strongly that in this particular debate, on the very sensitive issue of hospices, something I feel very strongly about myself Ivan Lewis behaved in a way it was not surprising it provoked a reaction."