He mentioned a not-further-defined mechanism for the EU to keep unlimited control over the UK. The actual claim was "it gives the EU effective control of the U

He mentioned a not-further-defined mechanism for the EU to keep unlimited control over the UK. The actual claim was "it gives the EU effective control of the UK economy without any mechanism for the UK to leave that arrangement without the EU's permission", which is quite a different statement to what you just wrote. In the context of the proposed Withdrawal Agreement, the mechanism in question is the proposed backstop, which as it stands requires an open border to be maintained and has no exit conditions that the UK could exercise without EU consent one way or another. The only ways to keep a fully open border established so far involve remaining within the SM and CU. Without quibbling over minutiae, the practical effect of that is pretty much what blibble wrote.