Travel newbie - passport query about Northern Ireland

Hi all,

I live in England and will be attending a friend's wedding in the first week of August this year.

My query relates to whether you need a passport to travel from England to Northern Ireland.

I know they're a part of the UK, and most sites say no, but I have read that it can depend on the travel company you go with.

I'm thinking of going with Easyjet who I think do not require passports as ID. I'll be taking my driving licence and national insurance card with me.

Anyone know for certain?