Hi,
Asda sell them as I'm sure all the large supermarket chains do but I got a rather nice plastic set (which float and are easy to clean) from Asda for the extortionate sum of 50pence....While your in there why not really splash out and get some of there plastic jugs (about 25p each) which come in really handy for so many things and a sieve (50p) which comes in very handy for washing gravel. They also sell cheap garden hosepipe (£1.99 for 20M(?)) which is perfect for water changing and 12Litre plastic buckets for a £1 last time I looked. A whole tub of sodium bicarbonate (baking powder) for raising KH will set you back 50p there to. Cheapskate, who me sir no sir. LOL.
Regards, Chris.