The big debate over Brexit now comes down to this: if the Irish backstop kicks in and the UK finds itself in a ‘temporary’ customs union with the EU, who will ultimately get to decide whether or not the UK can ever leave?

Brexiteers are deeply anxious that the UK will get trapped in this customs union, unable to set its own tariff rates and strike trade deals around the world as an independent country.

They argue that no serious country would give up the right to determine its own trade policy, handing the keys to its own future to a foreign trading power - the European Union.

Government sources indicate that Geoffrey Cox, the attorney-general, is briefing the cabinet on Tuesday on two different approaches to solving this problem: a unilateral right to walk away, or a dispute resolution mechanism, with an independent arbitration body.

Both of these ideas still need to be negotiated with the EU, so here we look at the conundrum now facing the cabinet - and the options open to Theresa May.

Just remind me, if the ‘Irish backstop’ kicks in, and we don’t like it, why can’t we just walk away?

Because at the moment the EU is insisting that, in order to get a Withdrawal Agreement and an orderly exit, we must sign up to an Irish ‘backstop deal’ which leaves Northern Ireland in the EU customs union and single market for goods.