Well she has survived a 550 mile trip around Wales in the pouring rain. She still pops ocassionally and stutters from time to time but no worse than before. I could not find any lose nuts/chain/tensioner bits as suggested. She needs a service soon so I'll get her booked in early so they can take a look and hopefully they can sort the problem before something goes bang in an expensive style.
Thanks all for the suggestions and help.
Cheers
Darren
PS Welsh Rally was a hoot, despite the weather!