You will get a better response if you post to the UK Wreck ferrets section or in the new to Scuba list.
As for getting started it depends if you want to dive the UK or not. If not then tie it in with your next holiday abroad and do a referral.
If diving in the UK, then find out which clubs/shops are near you, the main agencies are Padi, BSAC and SAA, each have a website that would tell you where to look.
If you have more than one option near you then try and meet the instructors and club members and see if they are you kind of people, if so then enrol on a Open Water/Ocean Diver course.
From what I have seen, it matters less what organisation you go for than the people and equipment you dive with.
As for the kit you would need to buy, you may not have to buy anything to start with, or maybe fins, mask and snorkel (£50ish). You should be able to borrow or rent the rest of the kit until you know what you like in terms of diving and gear. But wetsuit (not really for UK, £80 to £200), Drysuit (£500 +), Regs (£200 - £400), BCD (£150 - £500) , computer (£150 - £400), cylinder (£100+) and the list of other items is endless (knives, flags, SMB, tanks, reels, clips.........)
