SATELLITE-TRACKED pay as you drive' road charging across a European motoring super-state is only a decade away.

EU-wide equipment standards are already being discussed. There are already several European directives in place.

And Poole-based Siemens is likely to be the focus for some of the key technology.

"The government has said that it wants a national scheme to be implemented in around 10 years," said Siemens head of marketing Peter Preston.

"There are no satellite-based systems being used in anger for private vehicles but there are lorry-based ones in Germany and Switzerland and they are just a different type of vehicle."

This is the future of motoring - road charging based on how far you drive with extra penalties for daring to do so in town centres at rush hour.

A chip in your car will track your car, telling central computers where your journey started, ended and everything else in between.

And because it can track distance and time, it could calculate your average speed - so the satellites involved could effectively become giant space-based speed cameras.

The civil liberties implications are not pleasant, Mr Preston acknowledged: "The whole issue is one that the government is going to have to look at."

Creekmoor-based Siemens is at the forefront of road charging - having just completed "WEZ" - phase two, the western extension of the London Congestion Charge zone.

WEZ went live on February 19. For the Sopers Lane firm, it means £60 million over nine years - an estimated £20 million for the initial development plus a further £40 million for maintenance and ongoing operational work.

"WEZ is the biggest single project that we have ever worked on," said Mr Preston.

Siemens might be Britain's largest supplier of traffic management technology - accounting for 85 per cent of traffic control systems across the UK - but doubling the London Congestion Charge zone was still a major challenge.

"Automatic number plate recognition was a fairly new area for us so we had a highly skilled team of engineers on it, taking it to the next level.

"It is designed to be able to process up to one million licence plates per day.

"I don't think the need will take it that far, it is likely to capture between 250,000 to 500,000 per day."

And isn't the avowed object of the exercise to cut congestion and reduce traffic numbers?

"Exactly."

Like phase one of Congestion Charge technology, WEZ relies on cameras capable of reading car number plates.

Siemens has installed 659 cameras at 127 sites, predominantly around the perimeter of WEZ.

But there the similarity with phase one ends. Unlike its analogue predecessor, WEZ is digital. That makes it cheaper and potentially more efficient.

"We were not involved with the first system at all," said Mr Preston.

"They generally put cameras around the edge (of the zone), one or two in the middle and some mobile ones.

"The problem with that is that you need a full-blown analogue video system back from the cameras to the processing centre.

"So at the moment Transport for London incurs significant line rental costs."

But Siemens' new system for WEZ processes the data from the cameras in roadside cabinets so much smaller packets of data can be transmitted back on what are effectively ordinary phonelines.

However, the phonelines are far from ordinary - they are not part of the normal public phone network. They are designed to be highly secure with all data encrypted.

"They don't want the data going on the public network even though it is encrypted and digitally watermarked'," said Mr Preston.

The WEZ system has more than one camera at each site, to record number plates from different angles.

Data processors choose the best angle before transmitting back to the central processing centre. It has two computers "in case one goes down". They can be routed to a separate building "in case the first one goes up in smoke".

The new WEZ Congestion Charge area takes in Kensington, Notting Hill, Hyde Park, Knightbridge, Chelsea and Belgravia.

It is possible to cut across the two zones on a north-south route without paying, via the Edgware Road and Park Lane.

You may also escape being charged if you drive a car with foreign plates because the DVLA may not have reciprocal agreements with all its overseas counterparts.

It won't stop you from being clocked but it does mean that the government might not be able to track down your address, and so have nowhere to post the penalty notice.

"As with most things, you will never achieve 100 per cent accuracy, you will never achieve 100 per cent efficiency," said Mr Preston.

But that won't stop them from trying.