Jeremy Corbyn says he is visiting Brussels to "support the interests of the people of Britain" and ensure the country does not "rush headlong into no deal."
Corbyn is in Brussels meeting European leaders, a visit which is purportedly about breaking the current deadlock in the Brexit negotiations.
In an interview with the BBC, he said: "We're here to support the interests of the people of Britain in our negotiations with Europe.
"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. We cannot countenance the idea that we just rush headlong into no deal with Europe.
"No deal with Europe would be very dangerous for employment and jobs in Britain."
Corbyn also said he had met the Prime Ministers of Sweden, Italy and Portugal to discuss what he described as "a cooperative new relationship with our European partners."
He is reported to have said: "the British Labour Party does not see anyone in Europe as our enemies - you are our friends, colleagues & comrades".