You can activate the card in your home. All you have to do is unplug your sky+ box and plug in the box that you intend to take to France. There are 2 satellite connections on the sky+ box and only 1 on the ordinary box. It doesn't matter which connection you use. You say that you have a box and a dish. I don't know what size of dish that you have but one for the UK will not be powerful enough for the south of France. The following is a dedicated forum for fringe reception of sky. It is a bit technical but if you are not they will be gentle with you and explain what is necessary.
http://www.satellites.co.uk/satellite/sky-digital-uk-platform-astra-28-2e-fringe-reception-tech/

Hi
Thank you very much for the info,we intend to buy the dish and bits n bobs while we are in France from either Bricoman or Castorama,one of our friends down on site has done it many times and it seems to work fine,we are only taking the digi box/remote with us.I will have a nosey at the forum you have suggested.
Mandy