Mr Green is the president of the Leyland P76 Classic Car Cluband knows what he likes. He has lost count of how many of the much-maligned 1970s classics he and his sons own.

"We've got quite a few, more than 10," he says. "They're a beautiful car, an under-rated car from the start, and people who criticise them have never been for a good drive in one."

Mr Green and the other owners of Australia's 1 million cars made before 1986 face a problem. Many Sydney petrol stations have stopped selling lead-replacement fuel, and in seven weeks a nationwide phase-out will be complete.

About 10 per cent of the country's car fleet was built before unleaded petrol was introduced in 1986. Tasmania has the highest proportion of old cars and NSW the lowest.

Jack Haley, a vehicle policy specialist for NRMA Motoring Services, says about one-third of these cars can use unleaded petrol because they were made in Japan, which switched to unleaded many years before Australia. But this still leaves about 700,000 drivers who will have to use a fuel additive every time they fill their petrol tank.

Engines built to run on leaded petrol have soft valves and valve seats. The lead in older fuel coats and protects the valves; unleaded petrol does not, leading to the valves being inevitably damaged. The fuel additives now available contain potassium which, like lead, will coat the valves and protect against heat and wear.

Ken Dudley, founder of the Morris Minor Car Club, has been doing this with his 1959 model since leaded petrol came off the market at the end of 2001.

The 74-year-old from Sylvania, who prefers his Morris to his wife's new car, says he has "not had one problem" since making the switch and finds it only a slight inconvenience.