From
http://www.rootschat.com/links/01owg/Surnames
1.Under English law, a person may change their surname at will. The law concerns itself only with the question whether the individual has in fact assumed and has come to be known by a surname different from that by which they were originally known.So long as that is the case the change of surname will be valid. The process is not subject to any documentary formalities although there is a facility for doing so through the UK courts by way of a Deed Poll or Statutory Declaration.
Forenames
2.As long as it is not done for fraudulent or other unlawful purposes, a person may assume any forename without any formalities and can identify themselves with, and be identified by, the assumed name.There is some uncertainty in English law as to whether a Christian (Baptismal) forename can be legally displaced. A determination of a person's legal forename can only be made by a UK Court. However an assumed forename used in place of the name given on baptism is still valid for the purposes of legal identification if it is by this name that the individual has generally become known
