EDIT: Lloyd George comes to mind. That was over 100 years ago.
This was challenged as being in violation of the Acts of Union 1800 (particularly Article 6, which establishes an all-UK Customs Union) but the High Court ruled that the relevant parts of the Acts of Union are "impliedly repealed" by the Withdrawal Agreement Act.
There's a BBC article covering this here: https://www.bbc.com/news/uk-northern-ireland-57666255
With Brexit, the UK deeply and seriously considered constitutional change and decided to go through with it.
It wasn’t like they had some nefarious end in mind, realized the EU was getting in the way, and decided to withdraw to pursue this nefarious end.
They left the EU because they wanted to leave the EU.
Edit: I suppose it’s not really about Brexit, but about making trade agreements with the EU.