Jeremy Corbyn has arrived in Brussels to "make sure negotiations get on track" as he accused Prime Minister Theresa May of "upsetting just about everybody" in the Brexit process.
The Labour leader warned a 'no deal' scenario when Britain formally pulls out of the European Union in March 2019 would be "catastrophic" for the UK economy, but said he believed a deal "can be reached".
Mr Corbyn will meet three EU prime ministers in the Belgian capital, as well as chief Brexit negotiator Michel Barnier and European Parliament president Antonio Tajani.
"We're here to support the interests of the of the people of Britain in our negotiations with Europe," said Mr Corbyn.
"We're here to make sure that negotiations get on track, that we defend jobs in Britain and that we make sure there is trade access to Europe in the future.
"The prime minister seems to have managed to upset just about everybody and have a warring cabinet around her. It's up to her to get the negotiations back on track."
Addressing the prospect of Britain reverting to World Trade Organisation (WTO) rules should it leave the EU without a trade deal, Mr Corbyn said: "We cannot countenance the idea that we rush head long into a no deal with Europe.
"No deal would be very dangerous for job for employment and jobs in Britain.
He added that no deal would be "catastrophic for manufacturing industry and jobs" and create "real problems all through the economy".
"I don't want to see that, I want to see an agreement being reached.
"That's why we're here, that's why we're doing our best to ensure that an agreement can be reached, and I believe it can be reached."