British Prime Minister Theresa May has said it is "impossible" for her to rule out a no-deal Brexit.

She was responding to Jeremy Corbyn, after the UK Labour leader sought to block his MPs from helping the British government break a deadlock over its EU exit.

Mr Corbyn has instructed them not to "engage" with senior ministers until the Mrs May takes the threat of leaving without an agreement off the table.

He asked them to "respect" his own position and "refrain" from contact designed to secure enough support from cross-party MPs to get an agreement passed through the parliament.

Mr Corbyn has dismissed the cross-party talks as a "stunt" and urged Mrs May to "ditch the red lines and get serious about proposals for the future".

Seeking to keep up the pressure on the Labour leader, Mrs May wrote to him reiterating that she was "disappointed" at his refusal to meet.

File photo of leader of the British Labour Party Jeremy Corbyn | Image: Nick Ansell/PA Wire/PA Images

She said her door remains open for talks, but told Mr Corbyn on his "no-deal" demand: "That is an impossible condition because it is not within the government's power to rule out no deal."

Mrs May said this could be done only by getting a deal through parliament or by overturning the 2016 referendum result, something she was not prepared to do.

British Labour MPs had spent Thursday meeting senior government figures.

Mrs May will reveal her Brexit 'plan B' on Monday, after MPs rejected her deal by 230 votes on Tuesday.

She will then face a debate on it on Tuesday January 29th, with MPs getting a second chance to amend and vote on it.