[arp242]

> there are formal ways to register a name change, but it is not necessary and it is possible to "change" your name simply by having people refer to you using the new name.

Try opening a bank account like that. I can guarantee you it's not going to work; they will want to see a passport and proof of address with exactly the same name. I've been rejected by banks just because the utility bill shortened my second middle name to just "P".

This seems true for pretty anything of substance: government, tax, banks, insurance, health care, things like that. I'm not a lawyer and don't know how it works according to the letter of the law, but de-facto, you will have a "legal name".

[Y_Y]

I'm sorry you had trouble from your bank, I know the requirements are annoying. I have indeed opened bank accounts including in the UK and Ireland in names other than my passport name. It's easier once you have some piece of paper with a new name on it to get another.