In reply to tomshooter:
Regarding the avoiding tolls business, if you drive down via Belgium, Luxembourg, France and Switzerland you can avoid the tolls altogether, though you are supposed to buy a Vignette to use the Swiss motorways at about £30.
If you're going to the Swiss Alps or certain parts of the Italian Alps this makes sense anyway and even if you're going to Chamonix you can go over the Col de la Forclaz from Martigny and it only takes about 3 hours longer.
This also has the benefit of allowing you to fill up in Luxembourg which has some of the cheapest fuel in western Europe, currently about 25 cents per litre cheaper than France for both petrol and diesel.
Another tip is that you can use Tesco clubcard points to purchase Channel Tunnel tickets for free!
Post edited at 23:23