A big factor in the Brexit negotiations is the belief in the European Union that if Britain is successful outside the EU, this could lead to other countries leaving. So they are determined to try to ensure that Britain is hurt somehow.
So how likely is it that other countries will follow the UK's example?
Three big factors played a part in persuading Britain that leaving was viable. First, trade with the EU was falling. It was 64% in the year 2000. By 2007 it had fallen to 55% and on the eve of the referendum it was down to 44%. That meant that the majority of the UK's trade was with countries outside the EU, yet it was paying a substantial amount of money to the EU for access to the market. There is no point paying for something you arn't getting.
Secondly Britain was always a net contributor. That means that it would save some £15bn a year by leaving. That was attractive to voters who want the money spent on something else like the NHS.
Finally Britain controls both it's own defence (it is a nuclear power) and it's own currency. Some European nations feel they must be in the EU purely for the solidarity in defence. Britain has never felt this way. Indeed Europe hasn't ever helped to defend Britain But Britain had to intervene three times to rescue Europeans from tyrants: in the Napoleonic wars, in WW1 and in WW2. Britain also has one of the finest intelligence services in the world, and it shares this intel with the USA, Canada, Australia and New Zealand as part of the Five Eyes. It is notable that the Five Eyes are all anglophone countries and Britain's partners here are all outside the EU. Europe depends on Britain to share intelligence but Britain doesn't need Europe.
The independent currency and central bank are equally important. Most economists expected the British economy to collapse after the 2016 referendum result. Instead it sailed along thanks to the exhcange rate taking the strain, making British exports competitive again. It is easy to leave a union when you don't share a currency with them.
So which other EU countries have similar criteria?
One comes to mind: Sweden. The Swedes refused to give up the Swedish Crown, though currently they peg it to the euro. This means that they do have an independent currency and central bank which sets interest rates for the Swedish economy and doesn't have to take account of the rest of the EU.
Sweden's exports break down as follows: to Germany 10.4%, to Norway 9.5%, to Denmark 7.4%, to the UK 7.3%, to the USA 6.6%, to Finland 6.3%, to the Netherlands 5.1%, to France 4.9% and to Belgium 4.4%. The rest is made up of the smaller EU coutries and countries from around the world.
Once the UK leaves, 23.4% of their exports will go to non-EU countries (Norway, UK and USA).
That is still a very small amount going to non-EU countries, so they might want to stay just for trade.
Sweden is also a net contributor to the EU and this is where it gets interesting. Currently they might consider that what they pay is worth it for the trade they get back. But when the UK leaves, the contributions for the remaining western states will rise. How high the contributions rise is key. If the trend continues for the EU to demand more and more money continues, the Swedes might pull the plug, especially if they manage to increase their trade with non-EU countries.
It's possible we might see a two-fer with Denmark and Sweden leaving together. Denmark shares similarities with Sweden - it too has it's own currency and central bank, and pays a lot of money into the EU.
But as always it depends on whether the risk-taking Brits manage to pull off a glorious Brexit. If they do, envious glances will be cast with others wondering whether they can do the same. Which is what is worrying the EU.