Thanks for the various suggestions.
George, the clear plastic bags are for carrying the few items that are allowed, there's what appears to be a definitive list of allowed items produced by British Airport Authorities and it doesn't include film.
Sending film poste restante is a good idea but as I'm leaving tomorrow and it may take several days (including a weekend) to get there I don't really want to be hanging around Reykjavik rather than heading east. It's something I will be seriously considering in future though. As I'm camping I can't really arrange a courier to drop at a particular destination, especially given the very short timescale.(Been at work all day so haven't been able to arrange much other than a bit of sneaky forum use).
I've decided to take the film anyway, if it has to go in the hold I'll try and buy in Reykjavik, if I can find some then I'll write off the stuff I brought with me (20 quids worth of film isn't much compared to what the car hire is costing me!). If I can't find any I'll use what I brought anyway and if it has to be checked into the hold on the return I'll post it back. If I'm lucky it may come out OK, if not I'll still have what I shot on my D*git*l SLR, which is coming with me anyway as backup and for general holiday shots. One of the reasons I recently bought the MF camera was to take with me to Iceland, so it would be a shame to leave it behind.