Right.
I'm guessing that if you were coming down the A1 in Northumberland, you hit the camera at either Morpeth (Hebron.)or Belford, (If you estimate that you were about 80 miles from Auld Reekie.) both of which are standard Gatsos, and are of the rear facing variety. Gatsos flash twice when they are set off. Truvelo cameras are the one with the red lens in them and can be forward or rearward facing. As for film in Gatsos, the camera partnerships are moving towards digital Monitron cameras, so no film in these, but some camera partnerships have admitted that the Gatsos with film do get rotated.
The police have to raise an NIP, (Notice of intended prosecution.) within 14 days of the offence being committed, however if it takes 6 months to reach you, then that is irrelevant, it's the 14 days that's important here. You are then duty bound to return the form within 28 days stating who was driving at the time. Failure to do so is a further offence, and can net you a £1000 fine and 6 points.
For those of you that have sat nav, then if you haven't already done so, subscribe to the PGPSW camera database for your unit. The annual cost could be a saving in the long run, but if your like me and fortunate enough, then as a lifetime member and verified spotter, you get it free.
http://www.pocketgpsworld.com/
Finally guys. Don't blame the truck driver for doing 40mph on a single carriageway. That's all we are allowed to do legally. In this day and age of far superior truck design, the limits need changing to reflect this. More accidents are caused by impatient car drivers not realising that the truck driver is only obeying the law, and go shooting past into oncoming traffic.