The GRO is the easiest and cheapest place and covered the whole of England/Wales, you can apply online, pay and it is sent in the post to you,
https://www.gro.gov.uk/gro/content/certificates/Login.asp or if you need it immediately, you write out an application form available from the local registrar, pay and collect it that day or within a couple of days, it is more expensive to do it that way and you have to know which registry office to apply to( if you get the wrong one and they can't find it, there is no charge)