Check coin colour, if any coin is not the colour it should be, keep hold of it to investigate further. If it is a silver 2p or bronze 20p, see the images shown.
Check for coin rotation, the design on the coin should be the same way up as the Queen's head when the coin is turned over in the same way as the page of a book is turned. If not keep hold of it to investigate further, the image shown for the Britania £2 coin is one example of this error.