The EU, taken as a whole is the UK’s largest trading partner. In 2018, UK exports to the EU were £289 billion (46% of all UK exports). UK imports from the EU were £345 billion (54% of all UK imports).
The share of UK exports accounted for by the EU has generally fallen over time from 55% in 2006 to 43% in 2016, though this increased slightly to 44% in 2017 and 46% in 2018.
researchbriefings.parliament.uk/ResearchBriefing/Summary/CBP-7851
If we leave the EU without a deal should we just forget about 46% of our exports and 54% or our imports?
Remember the the EU is the worlds' largest and most successful trading bloc in the world, currently comprising the UK and 27 other member countries.
In negotiations, size matters. A single "third country" as we would be outside of the EU, could never hope to get as good a deal as we presently have.
If we want to trade with the other EU countries at all, it would HAVE to be on their terms. We would have to comply with EU rules whilst having no say in them.
One of the most misleading mantras of the lying Leave campaign was "they need us more than we need them". Not true. They might sell more to us than we do to them, but not in percentage terms. UK trade only represents about 8% of their exports, as opposed to EU trade representing 46% of ours. Clearly a lot of leave voters never understood this and still don't.