dawlish dave said:
Let us not forget that in countries taken over by Germany it was the local police that helped out in rounding up Jews. We in the UK sometimes take the moral high ground, but there would have been people in our country would have done the same.
It happened on The Channel Islands, where the authorities were totally co-operative, on the instruction of the Home Office, & British police, on instructions from the Germans, rounded up a number of alien Jews who were sent to their deaths. Most resident Jews had escaped to the mainland. Having said that, there were also people on the islands who risked their lives to shelter Jews.
A post-war British intelligence report stated:
When the Germans proposed to put their anti-Jewish measures into force, no protest whatsoever was raised by any of the Guernsey officials and they hastened to give the Germans every assistance. By contrast , when it was proposed to take steps against the Freemasons, of which there are many in Guernsey, the Bailiff [Alexander Coutanche ] made considerable protests and did everything possible to protect the Masons.
Coutanche was ordered by the Home Office to remain in charge and action whatever orders were issued by the German military authorities, even though he wasn't apparently keen on the idea. He also refused to authorise the order for Jews to wear a yellow star but in all other matters he co-operated as instructed.
So based on that, it would have certainly have been feasible that the Brirish civil authorities would have been largely co-operative in the event of a successful invasion.