i would say that to go for a humber boat around the 5 mtr mark would be a wise move, evry capable craft, although not as aesthetically pleasing as say a zodiac, they have a better hull. a valiant is also a good option, the 4.9mtr is a cracking boat, but steer clear of the vanguards, they are not meant for our waters! you could look at www.boatsandoutboards.co.uk
for ideas, or just use it to find ut various manufacturers of which it has a list on the site, which you can use to make a short list!
just in case you do end up looking for a zodiac i do have a zodiac pro 9 man for sale in as new condition, and its good in moderate chop, but in serious stuff it need longer hull length! i am loking for a larger rib around the 6mtr mark! it depends what you plan on using the baot for, because if general cruising, fishing, fuel efficiency, etc is in mind then a zodiac pro 9 for example would be fine, but if you want a more ruggedboat, the humber or a valiant4.9mtr would be better which although will have higher horsepower, and less efficient, will have advantages in the rough stuff, etc. let me know what you choose, or pm me if you need any mroe help! jonathan