Yes. Leave the European Union.
But you can be outside the European Union, and still be in the Single Market and the Customs Union.
The former does not preclude the latter.
But then you’ve not left it as you’re still bound by it , you might as well stay in it.
That’s like saying you pay membership for being in a union on the railway , but you get no vote or choice on any decision and you’re not allowed to join any other union , unless that union say yes.
There is no point to it , might as well stay in and have a say.
Leave means leave it really is simple , even I get that.