Facing a backlash from pro-Brexit cabinet ministers, the prime minister sought to dismiss fears that the “backstop” – keeping the UK aligned with the EU customs union – could become permanent.
Ms May repeated her claim that the “right solution” to the Irish border dilemma lay in a new overarching economic agreement to be negotiated.
And she said, of the backstop: “If it is necessary, it will be in a very limited set of circumstances for a limited time, but we are working on achieving that commitment to Northern Ireland through our overall relationship with the European Union.”
The comments came after Michael Gove signalled his unease about the backstop plan – which would see the UK retain EU tariff levels into the 2020s.
“The whole point about the backstop is that it’s intended not to be implemented, but it’s there just in case,” the environment secretary said.
Earlier, Boris Johnson issued his own veiled warning that the backstop plan – to be set out in writing to Brussels in the next few weeks – must not be a “betrayal” of the referendum vote.
Speaking to reporters on a trip to Latin America, the foreign secretary said: “Brexiteers fearing betrayal over the customs backstop must understand that the prime minister has been very clear that neither option is an outcome we desire – we want a deal with the EU and she will deliver it.
“I’m convinced that the prime minister will be true to her promises of a Brexit deal – that sees Britain come out of the customs union and single market, have borders as frictionless as possible, reject European Court of Justice interference, control immigration and free to conduct unhindered free trade deals across the world.”
However, it is thought unlikely that the EU will accept a time-limited deal, having stated the backstop must remain in place until another solution is found to avoid a hard border in Ireland.
The two alternative customs plans put forward – untested smart technology, or the UK accepting tariffs on behalf of the EU – have already been rejected by Brussels.
Furthermore, the EU is sceptical that the free trade agreement Ms May is seeking will be achieved quickly, or remove the need for border posts and checks.
The clock is ticking because the EU says the UK must sign up to the backstop in order to strike a Brexit deal and secure the transition period, through to the end of 2020.
Speaking during a visit in Cheshire, the prime minister said: “The European Commission between December and March outlined their backstop solution.
“That was unacceptable to the UK government, I think it will be unacceptable to any UK government because it effectively put a border down the Irish Sea.
“So, what we are proposing is an alternative backstop proposal but nobody wants this to be the solution that is achieved.”
The EU’s backstop plan proposed alignment of regulations across Ireland – but the government now hopes to extend that across the UK, for “a limited time”.