There's also some Luxembourg sim-card provider that gives you a flat rate across Europe.
(Radio 2 - Jeremy Vine Show - did a piece on it a week or so ago)
Or you could just read the document provided by Ofcom about Using Your Mobile Abroad
Web :
http://www.ofcom.org.uk/advice/mobile_abroad/
PDF :
http://www.ofcom.org.uk/advice/mobil...ile_abroad.pdf