There are issues with Turkey, which is in a customs union, although it is a partial customs union, so we can discuss our future relationship in areas such as agriculture and services. I refer in all humility to the shadow Secretary of State, Barry Gardiner, who put it best. He said of a customs union that
“as an end point it is deeply unattractive. It would preclude us from making our own independent trade agreements with our five largest export markets outside the EU”.
That was then; it is not the policy today.