Keir Starmer, Labour’s Brexit spokesman, is under fire after entering talks to work with a law firm that challenged the Government over EU withdrawal.

A Conservative MP accused Sir Keir of a “conflict of interest” after he was offered a job by Mishcon de Reya, the law firm that forced Theresa May to give parliament a vote on Article 50, acting for campaigner Gina Miller.

The role is expected to involve advising Mishcon's internal think tank and would not see Sir Keir working directly with clients.

But James Cleverly, the MP for Braintree, told Sir Keir that “members of the public will rightly detect a conflict of interest between your paid work for a law firm and your important role on the front bench”.

In a letter, Mr Cleverly also raised concerns over the Labour frontbencher’s membership of the privy council of senior politicians.

Sir Keir was granted membership last month so he could receive confidential briefings from the Government on sensitive aspects of the Brexit negotiations.

It is thought that Jeremy Corbyn will decide whether his Shadow Cabinet minister will take up the role. Discussions between the pair have not yet taken place.

Two years ago, the Labour leader voted to ban MPs from holding second jobs, in order for them to concentrate fully on their responsibilities as MPs.

In his letter, Mr Cleverly called on Mr Corbyn to “clarify” its position on second jobs, adding: “Your actions will be seen as hypocritical as your party states one position, but allows its own MPs to do another.”

Sir Keir, a former director of public prosecutions, worked for Mishcon de Reya before becoming an MP, joining the firm as a part-time consultant in its disputes practice in 2014.

He also held a similar position last year, receiving £4,500 a month for legal advice provided to the Mishcon de Reya Academy between June and September.

In 2015, Labour failed in an attempt to ban MPs holding paid directorships or consultancies. No members of the Shadow Cabinet have second jobs at present.

When George Osborne was appointed editor of the Evening Standard in March while still a backbench MP, Mr Corbyn said: “It's taking multi-tasking to an extreme level — what a joke.”