Almost 100 new speed cameras will be set up across Sussex to catch twice as many motorists.

Nearly two million pounds will be invested in the "Robot" devices which do not flash and work 24/7.

The digital cameras will replace the entire current fleet of old-style cameras.

Experts believe they will snare twice as many motorists because they do not require film and so never stop working.

A prototype is now being trialed by the The Sussex Safer Road Partnership.

The county has been selected as one of two test sites for new devices made by German firm Robot which are expected to be put forward for Home Office approval later this year.

The prototype has been installed at an accident blackspot on the A24 just south of the Buckbarn crossroads, between Horsham and Worthing.

It is the first in Sussex which does not use film. It can store images of vehicles caught speeding on a memory card or send them via the internet to a master computer, removing the need for staff to load and unload film.

Staff from the SSRP, which runs the county's speed cameras, said it was an inevitable step that all would shift to digital technology and a widescale roll out was likely to start within a year.

There are currently 60 fixed position speed cameras, 27 traffic light cameras and four mobile speed cameras operating in Sussex.

SSRP's communications manager Emma Rogers said: "We are happy to be supporting new technology. We will be looking at changing all of our "wet" film cameras. It makes sense to make the change when firms like Kodak are talking about stopping making film."

She said the partnership hoped the new style cameras would drive down accidents on the county's roads by ensuring people were more aware that they would not get away with speeding.

She added that the new devices were designed to be more visible to give motorists more warning.

The SSRP would not give a figure for how much each camera would cost and none was available from Robot.

Figures for the price of digital speed cameras have been closely guarded between partnerships and manufacturors but have been estimated at around £20,000 - close to the cost of the existing Gatso cameras.

At that rate replacing all of Sussex's fixed speed cameras and traffic light cameras would cost £1,740,000.

The cost of the machines will be met through the grant the partnership receives from Government - funded in part by revenue from its existing cameras.

Last year it issued fines totalling more than £4million and recouped almost £3million.

Opponents have hit out at the use of digital devices.

Anti speed camera campaigner Captain Gatso, from www.speedaholics.com, said: "It's policing by numbers ñ i.e. the number of pound notes they can extract from your pocket."

He said camera partnerships liked digital machines because they required next to no maintenance and were cheaper to run.

He added that they were preferred because staff would no longer have to regularly change film, often facing abuse from the public as they did so or being sent to dangerous positions.

He said: "When they are live and online they will be on 24/7 and for 365 days a year. They never run out of film, it will not be a lottery like it can be now for people who might think "have I got a ticket?", it will be a dead cert every time."

Motoring group RAC Foundation has extimated that digital speed cameras, which are being considered across the UK, will double the conviction rate for traffic offences from the current two million a year.

The second Robot camera is been trialled on the A3 at Kingston, London.

The Sussex trial will last several months and will include tests using memory cards and internet transmissions.