In a video for charity the Soi Dog Foundation, they speak over distressing footage of dogs being trapped and crammed into dirty cages, then being left to starve for days before eventually being killed.
The animals, which are often stolen family pets according to the charity, can be systematically beaten, skinned and boiled alive because of the belief that the adrenaline released during pain tenderises the meat.
In the campaign video, Dame Judi says: “I didn’t know that these innocent creatures are crammed into cages so brutally that their bones almost break, so tightly that they can’t move, and that they’re trapped like this for the smuggled journey, which can take days.”
Footage shows dogs being thrown into cages where they are left starving and crying, before being stacked on to lorries for transport.
Some are crushed or suffocated on the journey, while others starve or die of thirst.
The ones that survive are killed inhumanely in illegal abattoirs. One dog’s death is shown just off camera in the video.
Downton Abbey’s Penelope Wilton, who plays Isobel Crawley, Laura Carmichael, who plays Lady Edith and Peter Egan, who plays Hugh MacClare, also feature in the film.
Warning: Some viewers may find this video distressing
Gervais says that many of the dogs are rescued and sent to shelters in north east Thailand, which receive no government funding and rely on donations to continue their work.
“I didn’t know about this unimaginable cruelty, and neither do the majority of the people of Thailand,” he adds.
Millions of dogs have already died and thousands are currently suffering, according to the Soi Dog Foundation.
It is using the film to encourage people to back a petition asking the Thai Government to stop the dog meat trade. It has already been signed by more than 423,000 people.
Addressed to General Prayuth Chan-ocha, the Prime Minister, the accompanying letter emphasises the danger of eating diseased dog meat and transporting unvaccinated animals, which can carry cholera and rabies.
It demands that the trade is stopped along with the serving of dog meat in restaurants, a ban on dog skin products and increased funding for rescue projects.
The National Legislative Assembly is currently considering Thailand’s first animal welfare bill, which does not illegalise dog meat.
John Dalley, Vice President of the Soi Dog Foundation, said: “Thai people do not consider dogs or cats as food.
“Some ethnic groups and foreign nationals working in Thailand do, but this is no excuse not to make the practice illegal in a country where the vast majority of its citizens find dog meat consumption abhorrent.
“By not specifically making the practice illegal it provides a huge loop hole for the traders to continue stealing and trading dogs.”
The trade in dogs for meat and skin in Thailand is often linked to organised gangs, who export it to Vietnam and China as well as selling within the country.