Do you know if I'll have any problems exchanging GBP in Iran? Do they mind 50 GBP notes? I don't want to bring over only 20ies.. that'll be too much paper!
GBP is amongst most popular foreign currencies in Iran and I believe you will be able to exchange it easily.
I have no experience with exchanging GBP myself, however, I had no problem in exchanging 100,200ies of Euro (in Rasht, a rather small city in the Northern Iran); 50 GBP (or even bigger notes) should be fine! [ but anyway you should get used to carrying too much paper, as eventually in Iran you will! ]