Speed cameras must be visable for 60 meters for 40mph or less and 100 meters for anything above 40mph.
This is the Department of Transport rules for speed cameras
http://www.dft.gov.uk/pgr/roadsafety/speedmanagement/pdfdftcirc0107.pdf
That is the same pdf that was linked earlier in the thread, and indeed where I got this from:
This camera signing, visibility and conspicuity guidance has no bearing on the enforcement of offences. Non-compliance with this guidance does not provide any mitigation of, or defence for, an alleged offence committed under current UK law.Which obviously states, that you have no grounds for defence or mitigating circumstances if the
guidelines are not met.
That is my point, these are guidelines or best practice methods, not hard and fast rules/laws regarding how or where cameras are placed or how they should be signed. Indeed some signing/camera placement is at the discretion of the local authority, although I think if they don't comply they don't get some/all of the revenue raised
The statement from Psychoca "I'd be inclined to check the whether suitable warning signs are in the vicinty of the camera, as required... You may be able to get away with them under a technicality...." was what I was answering, not about camera placement.
Of course this is just my opinion and perception of what is stated in that government pdf, but I still think you would have a hard time getting off with a speeding offence because there was no little white sign within 1km of the camera.
You are still breaking the law regardless of whether a sign is warning you that you may be caught for it, therefore the only signs to be aware of, are the speed limit ones.
Tigers best chance of avoiding the tickets is whether or not the stretch of dual carriageway is sign posted at a 30 limit and/or has street lamps.