Just an update on this problem.
Its now very hit and miss, works sometimes , sometimes not at all.
But its now stopping me starting the engine-as the neutral switch thinks the bike is in gear it wont let me start the engine without the clutch lever being pulled.
Ive spoken to the dealer who supplied me with the bike and they are kindly going to send me up a new switch under warranty and i will replace it myself ( there isnt a yamaha dealer in cumbria now...!)
When i get the old switch out i will see if there are any visible reasons for it failing.
Stupid little fault but taking time to sort.