Re: Just popping over to Calais ...
Yea, but if they using the same operator or you could make calls to anyone in the EU like it was a national call
FWIW my network (E-Plus in Germany) has been offering this since the spring even on PAYG. Surprise, surprise I now use my phone more when I'm abroad.
Otherwise SIM cards from the Isle of Man or the Channel Islands seem to be the best choice.