THERE is a tea towel that explains the rules of cricket in an easily understandable way. It begins: “You have two sides, one out in the field and one in. Each man that’s in the side that’s in goes out, and when he’s out he comes in, and the next man goes in until he’s out.”

Similarly yesterday, Theresa May tried to explain the 12 rules of Brexit in an easily understandable way. In this strange game, Britain wants to play by only letting some in while keeping others out. That means it cannot be in, so it must be out, but it wants the benefits of being in even though it is out and not paying for being in. In being out, it wants to be more in than those who are right out, like Switzerland and Norway, but it could be in among Turkey, Andorra and San Marino who are technically out but also a little bit in.

And so Mrs May – who wanted to be in but is leading us out – brought clarity to Britain’s future position with our biggest trading partner.

She did make two very clear statements. Firstly, parliament will have its say on the final deal. If the referendum result was about Britain restoring its parliamentary sovereignty then it is surely right that parliament is sovereign on this vital decision.

Secondly, Mrs May said categorically that we are going to be out of the single market. To say this publicly was a bold declaration, although really it was the only logical conclusion she could reach after the referendum in which control of immigration was a big issue. The single market – to which 44 per cent of our exports go and from which 50 per cent of our imports come – depends upon free movement of people and as the British people voted against that, we have to be out.

But then she turned to the customs union. This is the EU agreement by which goods cross internal European borders without any tariffs or bureaucracy. It is also the organisation through which the EU has done 56 trade deals with external countries. It is the largest custom union in the world and that strength has allowed it to negotiate good deals but, just like any union, it doesn’t want members unilaterally striking their own deals.

British business would like to remain in the customs union but the nation also wants the freedom to do its own deals with countries like President-elect Trump’s US. So yesterday, Mrs May employed the cricket tea towel approach to hum and haa about whether her negotiating rule was to keep Britain in or out, saying we’d be prepared to pay a little to stay in it and even if we end up out, certain sectors, like the motor industry, would like to remain in.

Mrs May’s singling out of the motor industry must have been a deliberate nod to Nissan, which threatened to withdraw investment from its huge Sunderland plant in the wake of the Brexit vote. Sunderland exports half of its output, 250,000 cars a year, free of any hindrance into the EU and when Nissan announced in October that its new Qashqai would after all be produced at Sunderland, there was speculation about what sort of reassurances it had gained about a tariff-free future.

So Mrs May held out the prospect of the UK being both in and out – an associate or partial member – of the customs union. This hokey-cokey position is possible as Turkey is one of three countries which has negotiated such a deal, in which its agriculture remained outside.

Mrs May was similarly on a sticky wicket when saying we were coming out of the EU but would like to remain in science, innovation, crime, terrorism and intelligence collaborations with the EU, which immediately led to German mutterings that Britain was trying to “cherry-pick”.

Mrs May finished with a surprisingly stern ending. Reminiscent of a recent episode of Midsomer Murders in which an unfortunate character is killed by a fusillade of cricket balls, she aimed bouncers at those within the EU who might wish to impose a punitive deal on the UK. She even threatened that if the UK is bowled out cheaply, it might turn into a rogue economic state, a deregulated tax haven, sucking inward investment and jobs out of Europe.

It was a powerful ending to a welcome speech – even though much of it was obvious, we do at least know a little of how Mrs May intends to defend her wicket.

But despite that, her rules of the game of Brexit are not really important: it is the other 27 member states who will act as the umpire in deciding how much Britain can remain in while it is out.