The anwser is 5p coin in england it is rarley used its a fact i also read it in a book 
I think the 5p coin is relatively common in Scotland and England, I know I have a few Scottish ones from change in my wallet.
The rarest coin in England is the ?5 coin, which was made in honour of Princess Diana of England shortly after her death, not in common useage but technically should be accepted currency.
In my wallet I also have a few Pounds, a few Euros, a few dollas, and something called an "Imperial Septim". Don't ask.
