Help £5 note left me in tricky situation?

I went into the bakers and gave £10 note they gave me change which they gave was a old £5 note. i didnt know i went in to the butchers and brought tomato ketchup she gave me £4 change and accepted the old bank note. i then went to chemist and kwik save walking back she stopped me and said she couldnt accept the £5 i gave her. i have already left the shop about 5-10 minutes ago. she expects me to go in tomorrow and exchange the old note from her and give her a new note. do you think i should do it. i have just moved into the area and i dont want to cause trouble just i dont want to end up giving a valid note for something useless. with that i can buy nappies and baby jars with it. what bank branches still accept that. please can someone let me know from recent experience in 2007 form exchanging notes. i live in cardiff i dont have a bank of england here and no point sending note off. it will cost as much to send it off. what do i do?
Answer
Go into any bank, they will swop it for you (i did it a few months back - had the same thing happen to me).