Hi Prue
Just wondering if you ever found out Martha's surname? If not then why not try the new search on the official GRO website, which will show the mother's maiden name. I have tried looking for you but I don't know what the registration district would be so the following is just one of many possibilities:
Eleanor JOHN, (mother GEORGE), March quarter 1840, Lllanelly Union, Vol 26 p 551.
Diana