An enrolled deed poll is a deed poll that has been formally registered with the Royal Courts of Justice in London. Enrolment makes your name change part of the public record, published in The Gazette. The vast majority of people who change their name by deed poll never enrol it — an unenrolled deed poll is fully legally valid and is accepted by every major UK organisation, including the Passport Office, DVLA, banks, HMRC, and the NHS.
Enrolment exists primarily as a historical option and for people who want their name change to be part of the public record. There is a fee (currently around £42) and a short administrative process. You submit your deed poll to the Senior Courts Costs Office, and once enrolled, the change is published. One practical use case is if you were born outside the UK and some organisations require evidence that the name change is a matter of public record — though even in these situations, an unenrolled deed poll is usually accepted.
If an organisation tells you they require an enrolled deed poll, this is worth querying. The Passport Office, DVLA, and most banks do not require enrolment — an unenrolled deed poll is sufficient. If you have been told otherwise by a specific organisation, it is worth asking them to confirm their policy in writing, as front-line staff sometimes give incorrect guidance. This service generates unenrolled deed polls, which are valid for the overwhelming majority of name change purposes.