Hello there!
Was it on a reeeally tall pole?
It could be a RedSpeed device (made by a company with the same name). These are red light cameras when the lights are red and speed cameras at all other times. They are, I believe, easy to control remotely and so they can set the speed threshold very low for testing purposes, therefore being set off by most people driving along.
If it was one on a very tall pole (vandal proof, they say) then it'll be nothing to worry about. They will have photos of you driving through a green light and a recording of the speed you were doing. If you weren't exceeding the speed limit then they'll have a photo of you not speeding. Lucky them. I wonder if you can ask for a copy under the Data Protection Act?
Road safety = flashing bright light at people who aren't even breaking any laws... Yeah.