I've got the chance to go and greet some of those pesky Ptarmigans this coming autumn.
Coming from the UK, does anybody know what Icelandic permits etc I will need to bring a 20b shotgun into Iceland?
Does anyone know if 20b ammo is readily available for me to buy, or should I bring my own?

Thanks in advance...

I presume you will come here as a guest, invited by some Icelander.
If that is the case, it is simple,
If you got a valid license in your home country all you have to do is to apply for a hunting license at the UST ( www.ust.is ) and an import license for the gun, from the polis.
The best thing to do is to send a copy of your gun license to the man you are going hunting with and let him take care of the paperwork.
Concerning the ammo I would think it is available at most gun shops here in Reykjavík although most Icelanders use 12 G shotguns, and the most popular shotgun is the semiauto

Sölvi