Had a fall on the ice last week and my Wisper 905 survived very well except for smashing the gear change lever Little bits of plastic ratchet all over the road and I'm now locked in 4th gear, which could be worse I suppose...
Anyway, should this befall anyone else the part you need is a Shimano TX50 7 speed shifter, fairly cheap at around a tenner but not often in stock. Googling around I've found one in Windsor and will hopefully fit it next week.
Ouch.