Everyone may know this but thougth it worth mentioning. After the end of June in a few days the old £20 note will not be legal tender.
Banks will however still take it for a few months.
I only heard about this last week so i might not be the only one. Whilst i didnt have any in my purse i did find a couple in the house.
Try to particularly mention it to older relations as they tend to keep money in the house.
You will not be able to spend it in a shop and likewise they should not give you it.