A cross-Government analysis is expected to show that under the Chequers agreement, which forms the basis of her deal, the UK‘s GDP will be between 1 and 2 per cent lower over 15 years than if it had stayed in the EU.

However, in a move that will prompt a backlash from Tory Eurosceptics, the ministers are expected to argue that the UK will still be significantly better off than it would if it left without a deal.