The aim of the CBIR rating is to fly an aeroplane under instrument flight rules with a minimum decision height of 200 feet (60 metres).
If you want to use the privileges of the IR(A) at night and you only hold a PPL(A) you will also need to hold a Night rating.
The theory runs as saturday-sunday intensive classroom sessions, every third weekend, plus home studies.
3 - 4 months
10 hrs simulator training (FNPT 1)
20 hrs SEP
15 hrs MEP
If you have documented 5 hrs of Instrument instruction normally included in a PPL, and/or 10 hrs Instrument instruction from CPL you may credit this.