Ministers are planning new legislation that could override a key part of last year’s EU withdrawal agreement.
The move could change the nature of new Northern Ireland customs arrangements intended to prevent a return to checks at the border with the Irish Republic.
Downing Street said it was a standby plan in case EU-UK trade talks fail.
Meanwhile, Boris Johnson said that, if a trade deal is not reached by 15 October, both sides should “move on”, which would still be a “good outcome”.
Although the UK formally left the EU in January, it has continued to follow rules set in Brussels during a transition period – which ends on 31 December – while discussions over a long-term trade agreement continue.
Another round of talks – the eighth – begins on Tuesday, aimed at securing a deal to allow companies to trade without taxes or customs checks.
But Mr Johnson is expected to tell EU leaders it must be agreed in time for the European Council meeting on 15 October if it is to be in force by 1 January.
The UK has said it wants a deal with the EU which resembles Canada’s, which gets rid of most, but not all, tariffs on goods traded.
But Mr Johnson will say no deal means having a “trading arrangement with the EU like Australia’s”, using terms set by the World Trade Organisation. In practice, this would mean taxes on exports and customs checks.
“That would be a good outcome for the UK,” the prime minister will say.
During trade talks, the UK and EU have been at loggerheads over two issues in particular – the future of fisheries and state aid, the money given by governments to help companies.
The EU says the UK is trying to give itself an unfair advantage by applying different rules on state aid, but the UK insists it should have control over this as a sovereign country.
Michel Barnier, the EU’s chief negotiator, told French radio on Monday: “The British would like the best of both worlds – export their products to the European market on their terms.”