Those in the Cabinet who told the PM this week that we cannot accept a backstop which leaves us in a Customs Union indefinitely were right. They are also right to want the full legal advice on the draft Treaty they are asked to accept.
There is however a much easier argument to use against the vague proposals emerging. The UK must not seek to sign the draft Withdrawal Agreement to pay the EU £39 bn in return for the promise of 21 months or more of talks about a possible free trade deal. That would be a very bad deal. It would be worse for the economy than leaving without signing such a one sided agreement. We need to spend that money at home boosting our own economy. We do not need another two years of uncertainty. Many Conservative MPs would vote against that. It would need new legislation to permit it.
We did not vote to leave one EU Treaty only to lock ourselves into a new one sided one. Nor is the Future Partnership Agreement likely to be one any independent self governing democracy could sign.