If i was going to change my name onn my passport, would I need a deedpoll?

In the UK your name has to reflect the name you were born with or amended through legal means and can be supported by documentation (eg marriage certificate, official change of name, etc). This means that it must be done by more than a personal declaration and has to be done through an official means that tracks your identity from the person who was entitled to have the passport through to this 'new' person with a different name.