(Listening to poker analogies on radio)
But the negotiations aren't like poker. 
Everyone knows what assets (cards) the UK holds. The trade balance, our position in NATO, our GDP, the role of London in currency markets, it's all obvious exactly what cards we hold. Nothing will be revealed. We also know exactly what cards the EU, WTO & other countries hold.
It's pretty much tolerated even by rabid Leavers that UK wants Brit nationals in EU countries to be able to stay there, for settled EU nationals to be able to stay there. In principle, we want minimal future tariffs & passporting for the city, but not sure we can get any of those things.
So what is there to keep secret & not reveal? Is the secret about which parts we would sacrifice to obtain the others? Is the secret about where our red lines are? And what UK govt will publicly pretend to EU is redline but actually we would sacrifice in a flash to get something else?