We account for 3% of EU trade but they account for 13-14% of ours. That's a scale firmly tipped in their favour. We have a surplus in services trade with the EU and the surplus a far bigger factor (since 3/4s of our GDP comes from the service sector)..
A much forgotten fact - The UK has an overall trading surplus with the rest-27, once so-called 'invisibles' are factored in. All this talk of "They need us more than we need them!" is just the sound of someone whistling 'Dixie'!
But here are some facts that need to be taken into account -
1. The Civil Service has lost all its negotiating expertise and is 70% of the size it was when we joined 50 years ago.
2. Not one member of the present 'Brexit' team has ever negotiated a trade deal. That was all left to the E. Commission in the past.
3. The 'Brexit' team has not received any instructions as to preferred outcome from the UK government. That is because civil war has broken out between members of the government's front bench.
4. Dave Davis and his team seem to be paying a waiting game, one assumes, in order to wait out the result of the German election in Oct.
5. That means that there will be just 12 to 15 months for negotiations to be completed. Any deal will have to be finalised a few months before March 2019, to leave time for the rest-27 to all ratify said deal. And that assumes that all 27 states do indeed ratify any deal.
All the above would suggest that there can only be one of three outcomes -
1. Stay.
2. Norway, i.e. stay in all but name.
3. Geh mit Gott, aber geh! Und mach die Türe hinter Euch bittle zu! (Go with God, but go! And please close the door behind you!)