Do I need a lawyer for a deed poll?
No. See here:
I changed my name a few years ago, just printed off a declaration, got two coworkers to sign it, and then sent it out to change my passport and driving licence and then bank accounts etc. It was very simple, most organisations processed it with minimal nonsense.
No and yes. Under UK law for most purposes, you do not need an “official” to do anything with a change of name document. However, when I went to renew my New Zealand passport they did require a Notary Public to notarise a copy of it and that it was all “legit” (had to bring in my old named NZ passport, my old named UK passport, new named UK passport and driving licence for address check). It was £100 about 10 years ago for that process (and actually about 4 years after I got married and changed my name - my wife and I merged our surnames).