Chequepoint has very misleading advertising of 0% commission, make sure you enquire carefully as it turns out that commission for changing foreign currency into pounds is actually 9.8%!!
And they do not refund so make sure you are aware and happy of paying 9.8% commission ... which is extremely high... when you go to them. Most offer 0% commission on euros.
Chequepoint is a chain of bureaux de change with branches throughout the world. They offer many services including exchanging foreign currency on a commission free basis when selling it.