Lomon,
The card is A5 sized and published by the CAA, complete with its logo and a statement that it includes changes notified by UK AIP Amendments up to 1 Feb 07! It is provided with each new 500 mil chart (and maybe others). Thus I assume it to be an authoritive document.
Regarding "being unsure of local procedures" is concerned, I wasn't. I was merely doing what the Campaign's card told me to do!
As far as ringing Brize about it, it ain't that important.
Given London Mil's reference to the AIP, in future I will simply ignore said footnote and call up on the Zone frequency.
(Now why couldn't that be included on the card? Dare I ask?)