Chuff - fraid the 100 sterling (no pound symbol on this laptop keyboard) is clearly on the CAA website.
Often heard people saying applying for both CPL (usually done on a single) and I/R (usually on a twin) at the same time would save you one hundred pounds............so went to have a look at their price list (mainly because I didn't believe it).
The web-site says that you can open your CPL with EITHER the single engine that you did the CPL with, or the MEP from the I/R - but if you want BOTH, then it's an extra one hundred.
Not discretionary - on their site (no matter how much we disagree with them)