From the day you sign#
A deed poll takes effect when it is executed, which means signed by you in front of your witnesses and dated. From that moment your new name is your legal name. GOV.UK puts it simply: after you have made your own deed poll, you can use it straight away as proof of your new name.
There is no waiting period, no cooling-off, no approval and no registration. If the deed arrives in the post on Tuesday and you sign it on Tuesday evening, your name changed on Tuesday.
What "using it" means in practice#
You can sign in the new name, introduce yourself by it, and ask every organisation that holds your records to change them. Each organisation changes its own record when it receives the evidence, so there is a period when some records show the old name and some the new. That is normal and expected; the deed poll is what links the two.
What takes time#
Only other people's processes. HM Passport Office asks for a document that already shows you using the new name, so a bank letter or a payslip comes before the passport, and GOV.UK says to allow three weeks for a standard passport application. Until the new passport arrives, GOV.UK's advice is to book travel in the name on the passport you will carry. How long it all takes puts dates on each stage.
Before you sign#
Read both names on the deed letter by letter. Once signed, the deed cannot be corrected, and the date on it should be the day you actually sign, never a date in advance.
