Questions on naturalized UK citizen

Dear forum

I am asking on behalf of a friend, who naturalized last week after attending their ceremony and received their naturalization certificate:

They haven't appied for their first adult passport yet, could they still register to vote? Or do they need to get their UK passport first before they can register to vote?

And what govt branches/agencies do they need to inform about their recent naturalization? Such as HMRC, banks, mortgage lenders, etc?

Finally, they still have their ILR BRP card which expired on 31/12/2024, do they need to return it to HO within 5 working days? They heard HO telling people to keep their expired BRPs so are a bit confused on what to do?

Thank you.

Registering to vote doesn’t require a passport. Google “register to vote”.
It’s best to inform the employer and bank. Otherwise you only inform people if needed. There’s no compulsion. You do know that the UK doesn’t require citizens to register anywhere.
No need to worry about the BRP recommend friend keeps it which his documents.

Suggest he registers here and ask questions directly.

I updated my mortgage lender, my bank, my insurers, and that was pretty much it.