When is sterling not sterling

When it's Northern Ireland Sterling!  Seriously.  Am going to Birmingham today but before I even thought about heading for boat I had to get myself some sterling.  I tried one bank, then another, then another . . .  . WTF???  Some banks only get sterling in 'every now and then'.  Other banks will only give you sterling if you have an account with them.  Useful for tourists eh?  Then there is the bank that will give you sterling but . . . it's very expensive.  Still, got my sterling and seeing as how you can't use Northern Irish sterling in England, Scotland or Wales I had to convert that to English Sterling.  You with me??  So what happened next?  The fucking bank 'bought' my NI stg for 82p and sold it back to me at 87p.  No straightforward swap or anything.  I fucking hate banks.