With thanks to Michael, who was at the meeting, here is the latest reply from Tfl. It looks like Tfl like the car park option, but are worried that it could all take too long to get sorted out.
Dear Tom
Thank you for your email.
Following the meeting on 16 April 2008, Transport for London (TfL) is now considering two options for the downside.
As previously described in my initial response using the space at the base of the stairs is the first option. We are hoping to have outlined plans in two weeks.
The second option is to use the exit via the south end of the platform into the council car park. There are a few issues around access through Network Rail land by sub station; the movement of passengers near Driver Only Operation (DOO) screens and the safety of passengers walking through the car park.
Next step to finalise and ironing out the issue is to contact Network Rail.
TfL is however considering option 1 as it will be easier to progress in the time available to us.
I hope the information I have provided has been helpful. Please feel free to contact me should there be any future queries.