I used my neighbour and my wife's friend. There are several other people you can use Teacher, Solicitor, Accountant Business Partner as long as they know you personally and not your solicitor or agent.  Friends of family. Community member in your church mosque or Gym Centre.  Hope this gives you some idea.

Guidance notes clearly defines who can be your referee just find another one.  I am sure this person also can fill out a s a referee but Paul Pron will give you better advice.

Leave the passport number blank but if he has naturalised as a citizen then he will have a naturalisation number. Enter that in the space underneath and then immediately under that ( in the box provided) state that "I do not have a passport as I have not applied for one yet."

As long as the referee has known you personally for at least three years and is of good character ( not been convicted of an imprisonable offence in the last ten years)

Either that or find another referee.

One of the referee that I intend to use has not applied for his British passport, he has taken his oath in the ceremony. Because he does not have his British passport, what is to be filled in the application form (page 12, sec 6.6a ?

I have an appointment at NCS tomorrow, so an urgent answer would be appreciated.