Macski:
Just registered with a couple of agencies who demanded my passport, I blaired some of the numbers so if someone wanted to use it for wrongful purposes they can’t
They ask for your passport because they have to check by law if you have a right to work in the UK or face a huge fine, at any given moment they need to be able to show who is legally working for them just like any other company.
Whilst I understand you want to make sure nobody steals your ID that passport number is to check you are who you say you are, if you go to any middle to large employer they are all going to ask for a copy of your cards, NI number and a passport for an ID check