Didn't realize you're in the UK. With that in mind (if you have a lot of pocket change available) the best coated strings I've found for longevity and deep thick tone are the Optima Golds. Yes, they are gold plated and they last a good long time (2 or 3 years for a weekly gigging and every other day practice bass in my case). But they are darn pricey! A five string set cost me $125USD and that was before the $25 shipping fee. Fortunately I can now get these here in the states from BassStringOnLine but that wasn't the case until just a couple of years ago. I've been thinking about putting a set on my Thunderbird, but it's the Gold Anniversary edition and I'm afraid adding gold strings to a bass with a gold body and gold hardware will bling it over the top.
All I'd need next is a big gold clock hung on a gold chain around my neck, some gold crowns on my teeth, gold rings on every finger, a few million bucks in my pocket and a half dozen half dressed gold digging strippers hanging all over me. Hmmm, this is sounding better by the minute!