Paul, you have my sympathies. If yours were the red and gray locks in the south west corner I suspect they were cut on the 19th or 20th. If the thief or thieves gained access through the open gate and then pedestrian doors I don't think the CCTV will help, unfortunately.
I know it is of no comfort to you, but it may be of help to others, I think the steel U-shaped bike locks are the most difficult to cut and the wire cable ones the easiest. I have yet to see a broken or discarded U-lock.