(Confession: I used to work for the Transport Research Laboratory in Crowthorne, and was involved in some of the early studies on the Controlled Motorways System's effectiveness. However, the following comments are my own vague memories and shouldn't be taken to be the offical position of TRL, the Highways Agency, or anyone else who was involved in it all...)
As far as I remember, when the Controlled Motorways system was launched they had modified Gatso cameras - the modification just being that the speed limit to which they were set could be adjusted to match the variable limit signs.
The Highways Agency had to get an act through Parliament to allow the variable limit signs to be enforceable, and it wasn't until a few years later that they did the same for automated number plate recognition cameras (e.g. SPECS) - I certainly don't remember it happening before I left TRL to get a proper job (1997).
I guess the 30,000 number must have been part of the pre-launch publicity, and probably assumed a vast hoard of civil servants working around the clock to issue all the fixed-penalty notices!
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Bryan.