Henig, the UK Director at the European Centre for International Political Economy (ECIPE) and adviser to the UK Trade and Business Commission, says that such a move "means only limited reduction in bureaucracy around rules of origin, with accordingly modest benefit. In return the UK will have to implement the inbound part of EU trade policy with little influence and uncertainty for our existing trade deals."
And he points out something that our politicians often forget, that "the EU shapes allowable options for partners. Theresa May was offered a customs union, which Parliament rejected, but, with circumstances very different to the desperate effort to find a divorce arrangement, this is not on offer again."
There is a tendency to think the EU is a shop window with deals on display that Britain or other nations wishing to join the bloc can pick and choose from. It isn't. And far from it.
He says in Brussels the EU view on UK relations is that "goods cannot flow more easily than people" and "closeness must also mean meaningful financial contribution and widespread, if not necessarily complete, regulatory alignment. Attitudes to perceived UK cherry-picking remain firm."
The folks in Brussels and EU capitals are not blind to what is happening in Britain. They read the newspapers and watch parliamentary debates. They are well aware, after ten years or more, what Britain wants, and they're determined not to give in to our demand to cherry-pick whatever suits us at any particular time. It is a hopeless task.
He also points out another important point that has been a feature of Britain's attempt to mitigate the worst aspects of Brexit:
"Furthermore, UK leaders wanting this closer relationship are expected to make a proper public case in Brussels. The days of outward EU-bashing while privately asking for the benefits are over, not least as this provides no basis for political stability."
I am sorry to say this is something successive governments have been doing for decades. Publicly, they blame Brussels when there are grumbles about some EU legislation coming through that proves unpopular with the anti-EU tabloids, however beneficial it might be, for workers, consumers or the environment. Privately, they supported the policy wholeheartedly.
I really can't remember a leader since Edward Heath, who was prepared to forcefully argue the case for European integration. Even Blair deferred to Brown in 1999 when Britain decided to keep the pound in 1999. We have always been a semi-detached member, dragging our feet and going along reluctantly with the European project.
We could get away with it post-1975 after the first referendum showed a significant majority in favour of the EEC as it then was. I am not at all sure that EU members would welcome Britain's return to the fold without leading politicians making what Henig calls "a proper public case" for rejoining. The sad truth is that our leaders will need to show a good deal of enthusiasm, consistently, over several years and make that public case for rejoining. Until that happens, and it isn't going to happen under Starmer, I don't believe we can even start to dream.
Starmer squandered the opportunity to create a coalition of the Lib-Dems, the Greens and the SNP in Westminster and to show that there was (and still is) a substantial pro-EU majority in parliament. That won't be the case after the next election, and possibly not for years and years afterward.
Farage and Reform UK are on course to form the next government. They will make an almighty mess of things. Of that I am quite certain, and if Mr Brexit can't make a success of Brexit, it will sound its death final knell, but we will all be counting the enormous cost for decades.
As Henig says, "This UK government has shown preparedness to walk-the-walk on EU relations. Gaining further economic benefits now requires it, or successors, to talk-the-talk."
I am afraid there is little sign that anybody is prepared to talk the talk on Europe.
