I'm not sure about the UK, but these chips (better and larger ones) are available from DIGIKEY in the US. Relatively cheap as well - a 120 second version for $10.18 US DIGIKEY # ISD17120PY-ND
240 second for $12.00 DIGIKEY # ISD17240PY-ND

Or just do a search for CHIPCORDER on DIGIKEY'S site

I'm using both - they are excellent

These were discussed in a previous thread

http://www.picbasic.co.uk/forum/showthread.php?t=9365

Ken