Good on you!
We watch lots of 'em, especially from Acorn, BBC, and BBC America. Also a lot of Masterpiece Mystery. No streaming, just disks.
Love Endeavour.
Grantchester was okay but not worth sitting through a second season. (A lot of 'em are like that, of course.)
We're on Miss Scarlett and the Duke now, and so far it's a hoot.
Prime Suspect, with Helen Mirren, is a good little string of gripping yarns.
There are also some easy-going mysteries we liked a lot where a small town is a character, including Doctor Blake (Australia), The Brokenwood Mysteries (New Zealand), and Broadchurch (England).
The most twisted plot has to be Sherlock, with Benedict Cumberbatch and Martin Freeman. You really don't know what all is going on until the last episode. Great stuff.
By far the most over-the-top, and not exactly a detective story, though it's full of little mysteries and was inspired by Detective Comics (Batman, to be exact), is Pennyworth. Not for the queazy! We love it.
Last but not least, a couple that aren't Brit fare but are as good as TV mystery series get: Elementary (with Lucy Liu as Watson!) and Berlin Station, another that'll keep you guessing through the final season.