Theresa May is about to trigger Article 50 and go into negotiations with the other 27 European Union countries to sort out arrangements covering British trade with this huge market. It is a complete mystery how Britain is going to play its cards and Theresa May doesn’t want to give anything away.

However a fascinating post from Stewart Wood, a former adviser to Labour PM, Gordon Brown and later to Ed Miliband, suggests that she does have a strategy but it may be the wrong one.

Drawing from his experience  in Whitehall he suggests that Theresa May plans to draw from her experience as home secretary where she successfully negotiated an opt out on  EU police and criminal justice matters – choosing to opt back in to measures she accepted.

She plans to use this to apply to the whole British negotiation.

He writes : “Her plan is for the UK to leave the single market en bloc, but renegotiate continued access to it on preferential terms for some key UK industrial sectors as part of a wider free trade agreement. According to this vision, these lucky sectors would continue to enjoy de facto membership of the single market, but without the requirement to be bound by decisions of the European Court of Justice. Problem solved, our Prime Minister thinks.”

So will this work? Not according to Stewart Wood because the mechanism she is using does not apply here.

” So it can work again, right? Wrong. The strategy of “exit then cherry-picking” worked with the JHA decision in 2014 for a simple reason: it was set up as an “exit plus cherry-picking” deal in the Lisbon Treaty itself. It is a colossal error to think that the same approach can work in the case of Brexit – a negotiation of phenomenally greater complexity, played on multiple chessboards simultaneously, where interests between the EU and the UK are nowhere near as simply aligned, and where opt-outs have not been negotiated by existing treaty provisions.”

I gather Stewart Wood’s views are reflected in Whitehall thinking. But whether Theresa May is taking any notice is another matter.

What it does mean is that if he is right the Labour Party, Liberal Democrats and the Scots Nats are going to have a field day if they decide to hold the government to account. Also all the sectors – from the car industry, the financial sector and technology to name but a few – might vote with their feet to maintain unrestricted access to the EU. Interesting times.