Here is a complete suppliers list for the UK. I didn't even know there were so many but there you have it:
ALL ABOUT E-CIGARETTES UK - Recommended & new suppliers list
What I would recommend you get instead of the one you have now is a KR808D-1, if and only if you must have one that looks like a cigarette:
Creator/Volt/Revolution or
Electronic cigarettes UK buy Electric cigarette or E-Cigarettes online (both UK based vendors)
With those kits you'll see at least
three time the run time and a regulated 3.6v battery.
The ones you're using now are like using windows 95 compared to these. They're one of the oldest ones out there, but I wouldn't see it as a bad thing, at least you know ecigs will work out for you.
Like others have said though, you could get some higher mg rated nicotine content to use when you're out so it gives a better throat hit.