I can see that Sally-Ann has PM'd you so hopefully that has helped. As you say, if you search under "education" in the directory you get a lot of names!
My own suggestion would be that if you do need to go back to the BPS website look first for those that offer private services - sounds obvious but the directory includes all chartered psychologists (those that work for statutory services only, mix of statutory/private and private only).
Once you start to narrow it down look carefully at the wording given under "additional information" at the end of each entry - this will give you some idea of where the individual feels their own expertise is.
I would then be very upfront, get on the phone to several and explain what you are looking for and in the timeframe you need it. You might find that starts to considerably narrow your choices.
This is only my own opinion but I know when I started looking for a good ed psych several years ago I ended up with a much smaller list than it looked in the beginning.