The gathering drew EU-flag waving politicians, actors and activists -- all accompanied by their four-legged friends and united in their opposition to Britain's departure from the EU.
"Today's showing that this country just isn't uniting around any vision for Brexit and it's one way of fighting," he said.
The dog parade -- which attracted everything from Corgies and beagles to huskies and a giant Leonberger -- took place two weeks before a larger pro-referendum rally, set to be attended mostly by humans, planned for October 20.
But politicians from all parties have joined a growing movement for Britons to have the chance to say whether they have changed their minds.
"It's nice to highlight a serious point in such a fun way -- everybody loves dogs," said German university lecturer Flora Renz, 30. She has lived in Britain for a decade and turned out with Billy, a three-year-old beagle draped in an EU flag.
"I hope people are going to see some sense. I don't know if a second referendum is the best solution but anything's better than what's happening right now."
Human participants in the march, many sporting fancy dress and painted dog faces, assembled with their furry companions displaying pro-EU signs on their collars and backs, near Trafalgar Square.
The crowd pawed its way through the heart of the capital's government district, before they were set to gather for speeches -- and likely some dog treats -- in Parliament Square.
Organisers plan to hand in a petition to May's Downing Street office "signed by dogs and owners".
After Brexit, Britain may have to leave the EU's pet passport scheme, which allows registered pets to travel to member states freely with their owners.
The change will mean dog-owners are likely to face increased bureaucracy and need more preparation time if taking their canine companions to the continent.
Some at the march bemoaned that and other impacts of Brexit.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)