John McDonnell, the shadow chancellor, rallied trade unionist comrades in Trafalgar Square under the admiring gazes of Karl Marx, Friedrich Engels and Vladimir Lenin

Theresa May is preparing to accept that Britain will remain in lockstep with the European Union’s customs rules for years after Brexit in a deal with Labour.

Under the terms of a tentative agreement Mrs May is close to signing up to a long-term customs union with the EU in all but name in return for Labour supporting her withdrawal agreement.

Details of internal discussions began to leak as Mrs May gave her strongest hint yet that she was prepared to give ground. She told MPs that both sides now agreed on “some of the benefits of a customs union”.

It is understood that under the proposal, which has yet to be agreed, the government would agree to enter a “customs arrangement” with the