My girlfriend said she thinks she has gone through a red light today, i've gone back with her to the lights and there is no enforcment camera and she wasnt pulled over by the police, however that area does have cctv.
The answer of nil is wrong however it is highly unlikely. CCTV evidence can now be used to prosecute for traffic offences however this is not very widespread at the moment. Also there is a small chance that a passing bobby noted the offence and will send a summons through the post. This can be done for traffic offences. For certain offences however (including red light offences) they will have to post out a Notice of Intended Prosecution within 14 days. Note that that they only need to prove they have posted it, not that you have received it.
That happened to me once. I wasn't quite sure where I was going, so ended up getting a bit flustered and looked at the traffic light for the other lane which was on green. I was a bit worried about it at the time, but I think it's fair to say that mistakes do happen, and sometimes you ahve to put them down to experience.