Mark and Brian,
Many thanks - it looks very likely that it would be the C1 roundels, given the date of production of 465 (how much delay would there have been, if any, between an aircraft leaving the production line and being delivered to an MU - the airtesting and ferrying could take some days, presumably?) and the fact the 455 had them. My source for EP465 being involved in Pedestal was indeed First Light (and Spitfires - Malta Bound as G-BZ added to his post, though presumably the artist took the tail number straight from the book much like me!). Now that it turns out that the tail number was wrong, I'm a bit stuck - might have to pick another number from the ones Brian provided!
Thanks indeed for all the information provided.
TOTD