If there`s no deal we leave the Union don`t we?? What happens if we do revert to World Trade rules..great fear surronding this idea but I don`t get what the problem is..look forward to being shouted down by asking this question but no one really explains it when watching the news - which actually have given up on recently as it`s just so full of ego - the country`s interest has long gone by the way side...
WTO impose tariffs on imports and exports, so things likes car parts which cross several borders coming in and out of the UK from the EU, would be subject to several tariff interventions rather frictionless atm.
There would be non tariff barriers to trade with the EU, to do with standards on health and safety etc...as things stand as a member it's assumed these are sorted, as a non member 3rd country checks would need to be applied.
All of these things require an increase in bureaucracy and the need for greater border control, which is expensive and inefficient.
Much of the UK's trade is in services rather than widgets....WTO rules don't really apply here... financial services though don't like losing their passporting rights to the EU, hence why banks etc are moving some operations out of the UK.
In order to gain any benefits from the WTO, we'll need trade deals... within the EU there are already many in place with countries like Japan with others coming on stream, these will need to be renegotiated, so it means getting into bed with the likes of Xi and Trump from a position of weakness, whereas EU membership offers strength.
Although it may be possible to do some helpful trade deals, WTO will inevitably mean loss of EU trade... which as our neighbour and main trade partner is going to cause an economic hit, something like 8% of GDP is bandied about as a figure which is 2008 recession territory.... JRM estimates it might take 50 years for a rebalance and a chance to reap any benefits.