You have two things to think about - first, to import your friend's dog into Switzerland, see:

http://www.bvet.admin.ch/ein_ausfuhr...x.html?lang=en

Then, to bring a pet into the UK under the PETS scheme, see:

http://www.defra.gov.uk/animalh/quarantine/index.htm

If you have further questions the hotline for the PETS scheme is listed on the DEFRA website; the folks there are generally quite helpful.

A word of caution, though - the UK rules are stricter than the other EU states; be sure to follow the required steps exactly as stated. FYI, it takes about 7 months (rabies vac, titre test, then 6 month waiting period) to qualify if your friend hasn't started the PETS process already.

ETA - Mark is right; for a whole host of legal and practical reasons, it would be best to draw up a formal transfer of ownership or guardianship agreement with your friend before bringing the dog into Switzerland.