Welcome onboard, I lived close to you for a while and did a few years at Worcester college ( now living in Australia ).
I can't recomend the little zodiac pro tour 550 enough I bought less than two years ago. It's powered by the amazing little Yamaha f70 which I've clocked up nearly 500hrs of family adventures with over the last 18 months.
We use it for all sorts of things from scuba, snorkelling, spearfishing and gamefishing far offshore ( 50km + ). My youngest son aged 12 never liked boating as he suffers from seasickness and fears big seas, now we have the rib he loves heading offshore, infact he prefers the rough conditions since getting the rib.
Mine has a 100 lt underfloor tank which gives about 300km range and cruises well at 40kmh or 22 kts, flat chat it does about 60kmh or just over 30 knots.
I'm about to head away with the boat to do some Great barrier reef exploring, where we will camp on remote small islands and need to carry enough fuel and water for the 600km trip.
My boat was 4 months old when I bought it for $22000 which is about £14000 fully loaded with quality electronics and a heavy duty trailer.