Read on Twitter
The devil is in the detail. But ultimately the UK choice is whether (a) to accept a deal the benefits of which cld be withdrawn if the EU (after arbitration) later decides that divergence has in fact become too great for those benefits to be in its interests any more; or https://twitter.com/peston/status/1336633624825827330
(b) to refuse a deal, and those benefits, now (and before we have decided what if any divergence we actually want.
It’s a bit like someone who balks at renting a nice house they rather like because there’s a term in the lease that gives the landlord a right reasonably to refuse them having pets, even if they have no pets and aren’t sure whether they ever will.
In each case, the rational option would appear to be to take the benefits now: and if it later turns out that diverging/buying a pet is worth losing tariff-free access/your nice house at a later stage, at least you’ve enjoyed the benefits in the meantime.
PS in neither case is “sovereignty” plausibly at issue. The landlord is not stopping you deciding not to have a pet: she’s just saying that if you buy eg a huge barking dog that annoys the neighbours you will have to move out.
Similarly EU is not stopping UK divergence: it’s just saying that at some point divergence would mean that UK tariff-free access to its market isn’t in its interests any more.
Similarly, the protest “but this is tougher than EU/Canada” misfires. The landlord may not have imposed a similar pets clause on a tenant renting her country cottage: but if you are renting her basement flat, her interests in no barking dogs are a bit different.
Further thoughts in response to this comment. https://twitter.com/stephengrove19/status/1336673620488286208
