LONDON (REUTERS) - Through song and colorful costumes, anti-Brexit protesters on the streets of London are making their message loud and clear: Britain should stay in the European Union.

One protester says he's still hopeful, despite the country's recent vote to leave the EU.

"There are all sorts of channels for resisting it, via say the House of Lords, constitutional challenges, legal challenges, even the EU itself. Possibly a second vote, you never know," said academic Ben Fairburn.

British comedian Eddie Izzard says leaving the EU simply cannot happen.

"We have to make European Union work, we have to, otherwise the world will not make it. Those are the stakes," he said.

But British Prime Minister Theresa May has said there's no going back, though she has yet to invoke Article 50 to formally begin the process of leaving the bloc.

With the British parliament set to return from summer recess, anti-Brexit marchers here and across the country are hoping to put a stop to it.