Oh OK, I can't comment too much on Hove, I only really go there to watch the cricket and don't have a problem then.
Hasn't Hove always been dreadful for mobile signals on all networks? I know a couple of friends who lived there and had to go outside to get a signal.
Three did used to have a bad reputation because of their poor coverage and drop-outs. They're now one of the best for coverage (in the top 2 I think) and I've been very impressed with their customer service too.