Theresa May is facing a Cabinet revolt over her new backstop plan amid concerns that it will keep Britain in a customs union with Brussels indefinitely.

The Telegraph understands that the plan, which will be discussed by the Prime Minister's Brexit "war Cabinet" this afternoon, does not include a hard "time limit" or end date.

The plan, which is due to be presented to Brussels next week, is likely to be strongly opposed by leading Eurosceptics in the Cabinet. There have been suggestions that it could prompt more Cabinet resignations.

The Government is poised to make the concession in a bid to secure an all-UK backstop to avoid a hard border in Northern Ireland, removing the final major obstacle blocking a withdrawal agreement.

Boris Johnson, the former Foreign Secretary, has warned that the deal would turn the UK into a "permanent EU colony".

The proposal would see the whole of the UK remaining in a customs union with the EU while negotiations over a free trade deal take place, which Brexiteers fear could take years.