It is a challenge, since there was little what they did right but on fairness there was nothing what they could have done right. /1
Let's take the the notion of not invoking A50 on the day after the referendum: well, would have been clever if there was ever a chance of an inner UK consensus about a realistic approach. /1
Or agreeing on financial settlement and citizen rights in December: Sure, would have been great if there ever was a chance that UK doesn't pay or threatens rights of EU citizens. Can they do one of it w/o paying a price which costs them economically or politically their heads?
If not, they just granted something which they could never not grant. Even more: it was very late, too much bluster and not even clear what happens with non EU family members.
Commiting themselves to NI backstop? Often claimed it was TM's fault but commenters generally miss an important point: Ireland was straightforward & won't accept a border and veto a deal. It was never a real choice given the asymmetric character of the relation b/w EU & UK.
Again, conceding on something which they could never not agree to is not appropriate behaviour but a logical step given the circumstances and given the background noise now and then it's questionable whether UK is committed nor if they understand why they don't have a choice.
In short: there was little what they could have done wrong, sooner or later they would have come to those points anyway. Problem here is that on nearly every step the relevant domestic audience sees the opposite as right.
Which is result of a misunderstanding: it is thought UK is an equal to EU (they are not and powerwise they don't play in the same league). So each concession from EU perspective is natural, while UK believes it shows good will and should be given something for it.
Which they don't get, hence everything what HMG does will either p*ss off their home crowd or the ones they dealing with (which have the power to ultimately screw up UK's domestic audience).
In that sense, HMG will never be able to do something right. Whatever they do, they will be blamed for it sooner or later. A truly ungrateful task.
Ignore the numbering at the beginning ;-)
