Yeah, all the evidence seems to point to the border closures being a stupid, counterproductive attempt to close the stable doors after the horse has bolted and maybe shoot the messenger in the process. Unfortunately, there seems to be a bit of a push here in the UK to spin this as a necessary and inevitable measure that the government should have anticipated, including the closure of the border to road freight - which I think is a siginificant escalation compared to the previous EU border closures - for, basically, Brexit-related partistan political reasons.

Being a little more cynical, the strain probably started somewhere else in Europe and came across the border.

It's probably not a coincidence that this strain was first detected as spreading right next to the Dover crossing.