The UK is about to phase out both the current £1 coin and the old £5 note. Check for currency that looks like this:

On 28 March 2017 the old, all gold £1 coin will be replaced by this twelve-sided coin. On 15 October 2017 the current coins will no longer be able to be used in shops.

On 5 May 2017 the old five pound notes will cease to be used. The new notes are already in circulation. You can redeem them, for face value, by returning them to the Bank of England, in person or by post.