Anti-Brexit campaigners are planning to march on parliament on Sunday accompanied by up to 5,000 dogs to hound Prime Minister Theresa May into holding a second referendum on EU membership.

The "Wooferendum" movement will see politicians, actors and activists walk through central London with their pets.

"It might seem barking mad - but it's not as mad as Brexit," Daniel Elkan, who is organising the event, said in a statement on Thursday.

The dog parade is taking place two weeks before a larger rally - attended mostly by humans - planned for Oct 20 to demand a "People's Vote" that would allow Britons to change their minds.

May has ruled out a second vote, saying it would betray the result of the 2016 referendum and destroy trust in politicians.

But some members of her Conservative Party are calling for one and the main opposition Labour Party has not ruled it out.

Dominic Dyer, an animal welfare campaigner, said leaving the EU could be "bad for our pets" after the government warned a no-deal Brexit could mean dog owners requiring extra paperwork and veterinary certificates to travel to the EU with their animals.

"From a shortage of skilled vets and vet nurses to rising costs for animal health and pet food products and even the end of the EU pet passport scheme, Brexit will be disastrous for the nation's dogs and cats and other companion animals," Dyer said.

Labour MP Owen Smith said in the statement: "We look forward to a great turnout of dogs and people. It's about to unleash a bit of common sense to end this Brexit madness".

Labour former spin doctor Alastair Campbell has said will be attending with his Cavalier King Charles Spaniel puppy.

"We have to do everything we can to show the politicians that the country is not uniting around Brexit," he said.

The march route will include Trafalgar Square and the Whitehall government district before the canine protesters arrive at Parliament Square.

Organisers said they would also be handing in a petition to Downing Street "signed by dogs and owners".