How much does US pressure over Brexit hurt Boris Johnson?

Criticism from Congress shows the danger of a diplomatic dispute, writes Andrew Grice

Britain’s prime minister Boris Johnson attends PMQs on Wednesday (EPA)

Boris Johnson’s threat to break international law by overriding part of his EU withdrawal agreement has not only provoked a backlash from Conservative MPs and Brussels. It now risks a diplomatic dispute with the US Congress.

Four congressmen have dispatched a strongly-worded letter to the prime minister urging him to scrap his controversial plan to take powers to overturn the Northern Ireland protocol designed to avoid a hard border on the island of Ireland.

Democratic congressmen Eliot Engel, Richard Neal and Bill Keating, who all chair committees in the House of Representatives, and Republican  Peter King asked him to  “abandon any and all legally questionable and unfair efforts to flout the Northern Ireland protocol of the withdrawal agreement and look to ensure that Brexit negotiations do not undermine the decades of progress to bring peace to Northern Ireland”.