A number of local councils are signing up their Closed Circuit Television (CCTV) systems to the ANPR network. As long as the cameras are technically good enough, they can be adapted to take the software.
In towns such as Bradford, Portsmouth and Luton that means greater coverage for the police and more journeys captured and recorded.
John Dean, who is co-ordinating the ANPR network for the Association of Chief Police Officers, said: "It's the finest intelligence-led policing tool we've got.
"It covers so many different areas from crime reduction, crime detection to road safety and everything in between."
But not everyone thinks it is such a good thing.
A 'marker' on John Catt's car led to him being stopped by anti terror police
John Catt found himself on the wrong side of the ANPR system. He regularly attends anti-war demonstrations outside a factory in Brighton, his home town.
It was at one of these protests that Sussex police put a "marker" on his car. That meant he was added to a "hotlist".
This is a system meant for criminals but John Catt has not been convicted of anything and on a trip to London, the pensioner found himself pulled over by an anti-terror unit.
"I was threatened under the Terrorist Act. I had to answer every question they put to me, and if there were any questions I would refuse to answer, I would be arrested. I thought to myself, what kind of world are we living in?"
Sussex police would not talk about the case.
The police say they do not know how many cameras there are in total, and they say that for operational reasons they will not say where the fixed cameras are positioned.
Information Commissioner Richard Thomas, whose job it is to protect personal data, has concerns about the lack of regulation.
He said: "There's very little monitoring. I mean, my office has very limited powers.
"We have very limited resources. We are not actively monitoring that area. You're right to ask the question. No one's checking it at the moment"
The BBC TV series Who's Watching You? asked the Home Secretary, Jacqui Smith, to comment on the Commissioner's views.
"It's something that we will look at further legislation about where necessary," she said.
"I don't think we should lose sight of the very considerable benefits that this technology also brings us, brings law enforcement."
Recent research by Huddersfield University found that the public seemed to share that view. The study took place in Leeds as the ANPR system was being introduced. The vast majority supported the cameras if they caught law breakers, with only a few mentioning concerns about police surveillance.
The police themselves say they have nothing to hide and would welcome the introduction of a regulatory code. But that seems some way off - and for now this secretive system continues to watch us and continues to grow.
BBC Two's Who's Watching You will begin on Monday, 25 May, 2009 at 2100 BST on BBC Two. Or watch afterwards on iPlayer
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