Greetings,
You want a quality suit first and foremost. Then you want a very durable suit for wreck diving. You want a good fitting suit, and that means a custom fit suit -- unless you're lucky and can fit a stock suit. You want a shell suit for the adaptability. Good quality trilams and crushed neoprene suits are pretty tough.
I use an Abyss Pro Kevlar TX (made in Canada which could help you in price in the UK?) which is a crushed neoprene suits with a Kevlar shell, and it is TOUGH (commerial divers have used them for quite a while). These are going for $1900US for a custom suit, Kevlar knee pads, Apeks valves, BDM commercial zipper, one pocket, a whip, and a gear bag. It has neoprene wrist seals, so a bit of seapage isn't unusual (not enough to worry about), but that is dependant on individual people's wrists. IMO, there isn't a tougher, better quality suit on the market than the Abyss -- especially for the money.
www.abyssdivingsuits.com
Viking has a trilam that is pretty cheap (less than $1000US), but given that Viking is a leader in the drysuit world, the quality is probably top notch. If I was on a serious budget, this would probably be the suit I would buy. Unfortunately, I don't think it can be had in custom fit.
I don't particulary care for Viking's rubber suits for wreck diving, as they can puncture, but they do have a heavy duty suit that would probably be OK. Of course, you're looking at big bucks for their rubber suits -- $2000+US. One thing is for certain, Viking's rubber suit are renowned for not leaking, and are a favorite among commercial divers. Sometimes, you can find someone selling a Pro 1000 dirt cheap (less than $1500US new - regular $2000+), and that be a worthy consideration if you're on a budget.
http://www.dyk-brand.se/sidor/viking1.htm
DUI makes several very durable suits (CF200 most notibly), but they can cost a lot ($2000+). They do make a very flexible suit, the TLS 350, for under $1500, but I can't attest to its durabilty for wreck diving. The 350 is a favorite among cavers. I believe the tougher DUI's are also used by commercial divers.
http://www.dui-online.com/
Basically, there are some suits out there that can be very good from a range of prices. If I was on a budget, I would shop by name brands that I am comfortable with: DUI, Viking, and Abyss. I wouldn't buy sport diving suits or a neoprene suit (which can be very inexpensive, but aren't optimal at all, IMO). I would look at what commercial divers and technical divers are using. If budget is less of a concern, $2000-$2500US is a good range, as you'll almost certainly get a great suit for that kind of money.
Good luck.
Mike