What is the Brexit ‘trapdoor’ – and why does it matter?

Helen Lewis of The Atlantic had a good line about the idea of “getting Brexit done” on The Andrew Marr Show on Sunday: “It’s like saying, ‘I want to get childbirth done so I can get back to lots of sleep and reading lots of novels.’”

Simply leaving the EU will not free the UK from all the agonised debates of the past three years. They may diminish in intensity and drop out of the headlines for a while, but most of the hard questions will still be unresolved.

If or when the UK leaves, we will enter a transition period until the end of 2020, during which time we will be treated as if we were still a member. So all the concerns that Sir Oliver Letwin and Philip Hammond had about the danger of a no-deal Brexit on 31 October are only postponed, not averted.

If, by December 2020, the long-term trade deal with the EU has not been negotiated, it is not clear what will happen next. The transition period could be extended for up to another two years – that is, to the end of 2022 – by agreement with the EU.

But what if Boris Johnson doesn’t ask for an extension? John Baron, one of the Conservative MPs who actively wanted a no-deal Brexit, said in the past few days that he looks forward to Britain trading with the EU on World Trade Organisation terms – in other words, paying tariffs and abiding by the minimum regulations specified by the WTO.

This is a prospect that fills the majority in the Commons with horror. So Sir Oliver and Hilary Benn, the backbench heroes of the battle to block a no-deal Brexit, will swing into action again if the withdrawal agreement bill does go through parliament.

They will propose an amendment to require the prime minister to seek an extension to the transition period. This will be almost identical to the Benn Act, the law that forced the prime minister to send a letter on Saturday to ask for an extension to the Article 50 deadline.

Such an amendment is likely to be passed by this House of Commons – after all, the Benn Act was passed with a majority of 28 in the end. But what if there is an election that produces a different house? And what happens if the transition period is extended to December 2022 – by which time there has to be an election anyway – and there is still no agreement on a trade deal?

Boris Johnson, if he is still prime minister by then, might insist that he needs the threat of a no-deal exit from the transition period in order to have any negotiating leverage over the EU. Other MPs are likely to take a different view.

As Helen Lewis suggested, the idea that simply leaving the EU would lead to a period of unity, tranquillity and novel-reading is mistaken.