Getty Theresa May is set for a series of damaging defeats on the flagship Brexit bill in the House of Lords
It would mean tariffs on goods traded with the continent would stay the same post-Brexit, but would hinder the Government from signing new deals with other countries.
The Prime Minister has repeatedly said she wants to take Britain out of both the customs union and the single market.
Her stance has been spelled out in the EU Withdrawal Bill, which has cleared its first hurdle in the House of Commons after being passed by MPs.
But Ministers have reportedly resigned themselves to the fact the House of Lords will almost certainly pass amendments to try and force the PM to change her position.