so, its been in today, and had the following treatment:
Test drive found there was a hiccup as described.
checked for software update - needed update, so update applied, then test drive to discover slight misfire under hard acceleration.
Removed all spark plugs and checked - found cracks in all spark plugs !!!! replaced and tested ok.
Been washed very well, and cleaned inside, which has saved me a job, although not quite to my standards, but saved me several hours

Driven home (not far and all seems well). Given £25 in leisure vouchers as car been put in under warranty.
Time will tell.
