The government will introduce a new law that could change post-Brexit customs plans with the EU – but No 10 denied it would “tear up” the existing treaty.
The two sides agreed in 2019 on the terms of the UK’s exit, including on future trade in Northern Ireland.
Reports suggested a new law could “override” the legal force of that deal – the withdrawal agreement.
But Downing Street said it would only make “minor clarifications in extremely specific areas”.
The news comes at the start of another week of negotiations on a future trade deal between the UK and the EU.
The so-called transition period – which has been in place since the UK left the EU in January – will end on 31 December and the two sides are trying to secure an agreement to take its place.
But Boris Johnson said if a deal was not reached by 15 October, both sides should “move on” – meaning the UK would go on to trade with the bloc on international trading terms.