I was in Fopp Union St Glasgow yesterday and they were pitting out hundreds of T-shirts all reduced to £3. There were some hoodies too.
T-shirts were the official ones in small clear bag style packaging.
I saw Nirvana, Bob Dylan, Bob Marley, Misfits, Korn, Bullet from...., Lego Star Wars, Scarface and loads more. In S, M, L + XL.
Edit: Seems from the comments below that these seem to be £3 in most, if not all stores.