Yes the plug's good, in fact I cleaned it today just to try out my new plug cleaning brush!
Re our previous plug conversation - I've just ordered the NKG Iridium plug - BPR6EIX. It meets all the criteria of the Bosch code, and less than six quid delivered from Amazon so I didn't think it extravagant. It'll leave me the Bosch to carry as a spare.
Thanks for the backfiring link. I have changed the exhaust of course, and expected a bit of backfiring, but it's odd that sometime's it does it a lot and other times hardly at all.