So much for "we get to write our own laws" as per the Brexiteers. We'll just copy paste EU laws! I wonder how long it will take for those laws to be removed
We still follow several British laws in India 70+ years after independence. Unless, there is a demonstrable political benefit, old laws generally stay on the books.
UK law won't diverge from EU law if the consequence is loss of access to or friction with the European common market. The difference between the UK and the US in your comparison is that the US turned into the world's largest economy and sole superpower. The UK's economy is smaller than that of California.
Realistically you can only write your own laws if you're the top dog.
