You can use Isopropanol Alcohol. Get the highest pecentage avaible 90%+ is best so as not to leave any residue. Clean the lens
VERY gently with 100% cotton swabs (not the sponge/cloth kind used for make-up). Allow to dry for about 15-20 min (30+ if using less than 90% Alcohol). If that doesn't work it not your lens. The same Alcohol can be used on media discs(CD, DVD, GC, DC, PSP etc..) with cotton balls instead of swabs. Use 1 to apply and 1 to dry. I hope that helps.
P.S. The alcohol is usually less than 3$ a bottle U.S. If you in the UK I don't how much it would be there. Those cleaning solutions are just over priced alcohol usually.
Breaking Stuff=Fun!,Bug Testing<>Fun!, Bug Testing=Breaking Stuff, so...
Bug Testing=Fun! Hmmmm....
DOES NOT COMPUTE! SYSTEM MALFUNTION!