The myth that 50% of our trade goes to the EU is based on the Rotterdam Effect.
A UK company has a large export order for Brazil and it is sent in a shipping container. If that ship happens to call at Rotterdam to pick up more containers for Brazil then that is counted as a UK export to the EU. However it did go to the EU even though it was only passing through.
Maybe only 20% of our exports are to the EU. Imports from the EU are about £50 billion a year more than our exports to the EU. Our best export customer is the USA.
The 3 million job loss is a phoney threat. The Eu would keep trading with us as the sell some £50 billion a year more to us than we sell to them. We would pick up far more jobs from Free Trading with the Commonwealth and the rest of the world