we did it this summer from manchester. it took us about 12/13 hours with stops not including the ferry. I would take the Autoroutes which cost about 80 Eur going and as we came back via Geneva and on some of the more scenic roads it was about half that on the remaining auto route to Calais.
Note, if you are going Via Geneva, make sure you don’t go in the border queue for the 40chf vehicle vignette. we went in the other queue and no one checked that we had one.
if you are self catering I would highly recommend you stop at the hyper market in Sallanches as the supermarkets in Cham are massivly overpriced!
Go to Poco locos for a burger – you won’t be dissapointed!