Twenty-eight British women stretched and shed their shoes before piling into the car on the banks of the River Thames.
The event was spearheaded by Dani Maynard, who held the previous record of 27 people in a Mini.
The 28 women managed to jam into the car within 10 minutes. With all the doors and windows shut, they had to remain in the vehicle for five seconds for the new record to stand.
When the countdown ended, cheers erupted.
Maynard said their record was something the country could be proud of.
"I popped 28 women, not quite as easy as it sounds, but I put 28 women in that car to break the world record yet again for Britain," she said.
All the participants emerged from the crushing conditions unharmed.
Guinness World Record officials adjudicated the attempt and presented the team with a certificate to mark the occasion.
ABC News contributed to this report.