I'm disappointed that these other people are less than helpful: all you need to do is copy the following text to a document, print it out, and take it to your local police station, where they will be happy to help (fill in the bits in angled brackets as appropriates):
On <date>, I <your name>, of <your address> failed to stop at the <location> traffic lights, although they were red.I have no excuse, and understand that I may be prosecuted for the offence.
Make sure you sign and date it.