LONDON — Every morning, Giles Hacking gets into his Mercedes CL500 in West Kensington and drives to his office across town near London Bridge.

Sarah Hacking piles the three children into a Jeep Cherokee and drops them off at their schools. Often, her mother pitches in and delivers one of the youngsters.

Soon, though, multicar families such as the Hackings may be wishing all they had to contend with was London’s $8-a-gallon gasoline. In an unusual municipal experiment aimed at fighting global warming where the rubber meets the road, the British capital in October is to begin imposing a $50-a-day carbon emissions fee on every gas-guzzling private vehicle driven in the central city.

Even for the Hackings, who live in one of London’s better neighborhoods and earn a good income that will be a significant jolt: $100 a day for the school and work runs, $150 if grandma gets involved.

“It’s outrageous,” Ms. Hacking said, expressing a sentiment that appears to elicit a strong amen from many of those here who drive the big sport utility vehicles that Mayor Ken Livingstone refers to derisively as “Chelsea tractors.”

“We’d have a massive loss if we tried to sell our cars. And I can’t have a tiny little car because I have three children who go to three different schools,” she said. “At the moment, we just have to pay. We really have no choice.”

The new fee, adopted by the mayor after a long consultation with the public, has prompted threats of a lawsuit from Porsche and anger from many London drivers, some of whom have vowed to make it a central issue in the campaign leading to the mayoral election May 1.

For five years, London has been assessing drivers a daily “congestion charge,” now set at $16, to drive into the central city and a large swath around it, a fee designed to tackle the infernal bottlenecks that have turned much of London into a parking lot.

Under the new experiment, drivers of the lowest-emitting cars would no longer have to pay a congestion charge to enter the central city.