im getting what i describe as a rattly diesel sound when my engine is idling and this has only started since using tesco 99 any ideas what the rattling is?

It could be something similar to the problems the first Shell "premium" fuel caused more or less anything?

well my next fill up will be back to vpower, ive tried tesco 99 for 2 tanks now (one to get used to it and the other to get a reading). found it about the same for mpg, but booting it it kinda goes flat about 3.5k rpm to 4.5k rpm then power comes quick quick (on the few boots ive done). No difference really around town so yes back to v power where i get a better reward scheme.