Like in France, and other occupied countries, you'd see POWs retained as slave workers except those released as useless (sick/wounded) and those released for political reasons (family members of collaborators). You'll see deportation of large numbers of workers for German industry/farming, skilled machinists for example. Naturally products of British industry and agriculture will cross the Channel, and Dicke Herman and others will be adding to their collections from museums and private homes.
There will be several groups who will be targeted over and above all of this. Jews, Gypsies/Travelers, Poles and Czechs who were refugees and/or members of forces in exile will be targeted. For starts British Jews (citizens) will be wearing the yellow star, forced out of any positions of influence and business. Non-citizen Jews and the Slavs will be deported pretty promptly, in 1940/41 the Wannsee Conference has not happened so death camps are not up and running. I think eventually British citizens (Jews, Gypsies) who are destined for extermination will be deported to camps in the east much like Jews elsewhere in western Europe. Setting up extermination camps in the UK would be very difficult to hide, and would not be well accepted by the locals as well as details getting out to neutrals/USA pretty quickly. What goes on in the General Gouvernment in what used to be Poland stays there.
There was the Black List, including both Britons and exiles in Britain. Those, and others will be dealt with locally - there will be concentration camps (not extermination camps) and summary executions for the Black List folks as well as others.
I wonder what will happen to Ulster? would the Germans gift it to Eire, perhaps in exchange for air/naval basing rights or would they occupy it lightly counting on locals to run it?