Hi,
One possibility I can think of :
"The Sherwood Foresters" was a British Army Regiment. They served in the North African and Italian campaigns during WW2.
If your grandad was in this regiment perhaps he was taken prisoner, later escaping from a PoW camp, (as many did after the Italian surrender) and making his way to Switzerland (which was neutral territory)?
I don't know what records were kept of ex PoWs arriving in Switzerland but perhaps somebody else can help here ?
Good hunting !
Maec