I have obtained Leave to Remain in UK for Indefinite Period in 1993. Since then, I lived in peace, working and paying tax, council tax, Pension and NI. Recently, I started thinking of changing job and approached some recruitment agencies. Out of blue, bomb dropped

I was told to obtain BRP if I have permit to remain in UK indefinitely in my old passport.

1 I understand this topic popped up in the past but it was inconclusive. Is switching from the sticker on old passport to BRP card compulsory? New employer might want to see it, but I might go for freelance, self employed. In that case, I am responsible for my own employment. I phoned immigration office, emailed several mail addresses but have been sent in circles. One woman told me while I could pass with old passport and the latest one at border control, I must obtain BRP. When I questioned further to clarify, she repeated the same answer and did not give me a clear answer and got quite rude. Other man told me not to worry about it until my current passport expires. It doesn't make sense either as my current passport does no longer carry a stamp. Nobody seems to listen or read email properly

Do they really understand English?
As it is very expensive to obtain one and the process seems quite painful, reading the forum, and I am extremely worried about sending all passports of 20 years by post even registered, half of me think I could do without one if it's not compulsory.

2, supposing I apply for one, the form for the person who already have the Indefinite permit, asks BRP ref no in Question 1.12. Other question such as NI have added part 'if you have one' but BRP Ref no does not have 'if you have one'. Where should I get the ref no. if I don't already have one? Since they charge the fee first before they start reading the rest of the form, I do not want to have it rejected on the base of lacking BRP ref no.
I very much appreciate it if somebody could shed a light on this issue. Thank you