Below is the letter he sent to the prime minister, as reported by Reuters:

"Dear Prime Minister

I am writing to let you know that I believe the talks between us about finding a compromise agreement on leaving the European Union have now gone as far as they can.

I would like to put on record that the talks have been conducted in good faith on both sides and thank those involved for their efforts to find common ground.

The talks have been detailed, constructive and have involved considerable effort for both our teams.

However, it has become clear that, while there are some areas where compromise has been possible, we have been unable to bridge important policy gaps between us.

Even more crucially, the increasing weakness and instability of your government means there cannot be confidence in securing whatever might be agreed between us.

As I said when we met on Tuesday evening, there has been growing concern in both the Shadow Cabinet and parliamentary Labour Party about the government's ability to deliver on any compromise agreement.

As you have been setting out your decision to stand down and Cabinet ministers are competing to succeed you, the position of the government has become ever more unstable and its authority eroded. Not infrequently, proposals by your negotiating team have been publicly contradicted by statements from other members of the Cabinet.

In recent days we have heard senior Cabinet ministers reject any form of customs union, regardless of proposals made by government negotiators. And despite assurances we have been given on protection of environmental, food and animal welfare standards, the International Trade Secretary has confirmed that importing chlorinated chicken as part of a US trade deal remains on the table.

After six weeks of talks, it is only right that the Government now wishes again to test the will of Parliament, and we will carefully consider any proposals the Government wishes to bring forward to break the Brexit deadlock.

However, I should reiterate that, without significant changes, we will continue to oppose the government's deal as we do not believe it safeguards jobs, living standards and manufacturing industry in Britain.

Yours sincerely, Jeremy Corbyn"