The controversy over whether to ban smoking in pubs has spilt over into the Liberal Democrat leadership battle.
The issue, which has also divided the Cabinet, produced the first sparks of a previously low-key contest.
Divisions also opened up between the four contenders over future funding of the National Health Service and how many seats the party should aim to win at the next election.
And Sir Menzies Campbell, the Liberal Democrat deputy leader, disclosed he was to swap his gas-guzzling Jaguar for more environmentally friendly transport.
The campaign's first studio debate comes with Simon Hughes, the party president, installed as the bookmakers' early favourite, closely followed by Sir Menzies. Mark Oaten, the home affairs spokesman, and Chris Huhne, the economics spokesman, hope that their exposure during the seven-week contest will help them to close the gap on the front-runners.
The four broadly agreed on a series of subjects and all said they would offer Charles Kennedy a prominent post in their frontbench team. But they clashed in the Sky News debate over how they would act in the forthcoming free vote on outlawing all smoking in pubs and clubs.
Sir Menzies said he would vote for a total ban as it was, on balance, the correct step. He said: "The public mood has changed very dramatically and I don't think it's right to expose people to a risk to which they aren't voluntarily assuming."
But Mr Oaten retorted: "I can't support an outright ban. I'm a Liberal ... if you are going to be a Liberal, Ming, you can't pick and mix which subject you are going to be Liberal on."
He was supported by Mr Hughes, who said: "My instinct is always less legislation, less regulation. Personally, I won't be voting for the smoking ban."
Mr Huhne denied it was a classic Liberal issue. He said: "This is a case of avoiding damage to other people. We have very clear medical evidence now about the effects on passive smokers if they are inhaling smoke."
On the health service, Mr Oaten, who called for "tough Liberal solutions" to attract voters, insisted patients should not have to pay for treatment. But he added: "If they can get an operation in a private hospital quicker and the NHS can pay for that, then we must consider that."
Sir Menzies said the private sector should only be used for services not available through the NHS, Mr Huhne called for greater local control of hospitals and Mr Hughes said the NHS has to be built up so patients did not fear having to pay.
With all four candidates arguing for tougher action to defend the enviroment, Sir Menzies was challenged to justify driving a Jaguar. He replied: "I have one 20-year-old car which has been my pride and joy. But we're all going to have change our habits, including me."
Asked how many seats the party should aim to win at the election, Mr Hughes replied that at least 100 would give them a share of power.
But Sir Menzies said there should be no glass ceiling on their ambitions and Mr Oaten said: "Over 300 seats to get us into government."