I've done a few halfs now some of these might be what your looking for but for some of the smaller races they will be club/local run so they won't be sorting race details till after Christmas.
Longhorn is a good one to start will if it helps in no particular order some of the best ones I've done are below. Some of them are a bit hilly and a few are just outside where your asking for but worth the travel. Put rough dates when can remember them
Buxton (may) - one of the best and hardest half's in the uk
Sheffield (date varies) - nice big city race only one hill but it goes for miles.
Eyam (may) - didn't run this year but hopefully will be back been having a comedy argument for years about if this is harder than buxton.
Leek - It's leek it's going to hurt.
White peak and tissington trail halfs - Both excellent halfs will sell out fast
Liversage (feb) - know it's in yorkshire but it's lovely low key and not many decent races around that time of year.
Nottingham (sept) - big city race but a cracker
Worksop (Halloween) - really nice friendly race
Clowne (nov) - same as above
Leicester (oct) - only done the marathon but if the half is as good worth a look
Lincoln - First one this weekend will shout up if its good got high hopes because of the organizer's.
Birmingham (oct) - also a big city race only one hill on the course and it's not a big one although some of the local's are scared of it for some reason.
Just in case there was a issue with the t-shirts not being delivered on time for Daventry Sprint tri. T-shirt's were posted today and there are well nice much nicer than I would expect for a sprint tri.