the rough premise for an embryonic AH is that at some point in last few hundred years seismic activity (yes there has been some) caused Dogger bank to rise the 25m or so it needs to to become an island.
Because of its strategic location (and oil and gas) its been populated and drained etc - with a population density same as Netherlands would have population of around 7.5m mix of immigrants from all countries round north sea. .
so the challenge - its 1940ish neutral (in same way as Netherlands) but broadly friendly to UK and suspicious of the Nazi threat.
It needs a north sea navy - trade protection probably limited to coastal/intra-north sea trade.
thinking MTBs and 'fishery protection vessels' (small destroyers) but suspect that AA capabilities more important than ASW ?
had a afterthought - maybe a coastal defence ship/monitor as fleet flagship
its a bit of a fun challenge really don't worry too much about plausibility.