Happened again on saturday morning as I was pulling into the local BP servo, though not as pronounced.
Both times at low speed low revs.
I have checked all the obvious things :
* Sprocket nuts - both front and rear
* Wheel alignment
* Rear axle nut
* Cleaned up all the horrible black greasy sludge that accumulates around you front sprocket area
* Made sure the chain link was ok.
Both times the daily temperature was pretty high Sunday - 42 degC, Saturday - 32 degC.
Have noticed that gear lever action isn't as fresh as it should be.
Have a horrible suspicion that maybe the dogs are worn in the gearbox, though you wouldn't describe the sensation as it jumping out of gear.
Will have to keep an eye on it and see if it happens again and with what frequency.
If Kev still has that motor after Xmas, he might well be getting a call from me
Bob