Hey there, we're from round your way too.
So a search on lowering and check the stance thread to decide what way you want to drop it (there's pros and cons to all of them, trust me, there is no perfect answer :lol: ). If you have a brave pill moment, then dropped spindles (T-haus or T2D) or Red9 will get you the drop you're after with bolt on goodies and you'll find proponents / critics of both. For the record, I'm on T2D dropped spindles for a 3.5" drop, close enough unless you're after really slammed?!?
For places to do the work, there's Retrocustom up in Baldock or Luke at Terrys is an easy run from Watford. There may be others, I'm just mentioning places I've actually used and trust. The other option is to talk to Paul at T2D about the one day lowering service, it's not a bad run from round here.