The DUP has threatened to unite with Labour to back a customs union this week as it warned it will unleash “guerilla warfare” to bring down Boris Johnson’s Brexit deal.

In a move that could torpedo the Prime Minister’s strategy for delivering Brexit by Oct 31, senior DUP figures have threatened to back proposals which could prevent the UK from pursuing its own trade policy.

Should MPs back an amendment for customs union this week, Mr Johnson could be forced to pull the legislation required to ensure the UK leaves the European Union on time.

On Sunday night a senior DUP figure told The Daily Telegraph there were “multiple scenarios with multiple options for us to resist Johnson’s anti-UK deal,” adding: "It will be parliamentary guerilla warfare."

The warning came after Sir Keir Starmer, Labour’s shadow Brexit secretary, invited the DUP to meet to discuss amendments to the withdrawal agreement bill, stating that the party’s “door is open”.