A drivers' lobby group has called on every motorist caught on a speed camera to ask for their case to be postponed – because they might all be thrown out on a technicality.

And if a series of legal challenges succeed, millions of speeding fines might have to be refunded.

The Government and police chiefs have dismissed the challenge as a red herring. But the Association of British Drivers (ABD) is aiming to challenge the legality of most speed cameras in the appeal courts in the next few months. It will argue that since the 1990s, the Government has failed to properly authorise new speed camera devices, which means the police cannot use them to take motorists to court.

The ABD claims the issue is so serious that drivers caught speeding now could quite legitimately ask for their case to be postponed until the legal challenges are resolved.

They have already won one case on that basis – magistrates in the Midlands threw out a case after hearing the speed camera used to clock the driver had never been sanctioned by Parliament.

But the Government and police forces across the West have dismissed the basis of the challenge and its chances of succeeding.

The ABD said the issue concerned the process by which speed measuring devices that have come into use since July 1992 have been authorised. Since that date, the organisation claims, the Secretary of State has no longer been empowered to approve the devices without laying a Statutory Instrument (SI) before both Houses of Parliament in each individual case. This has not been done, the ABD said, meaning that the evidence from these devices is not admissible in law.

The ABD's traffic management adviser, Malcolm Heymer said: "This is not a trivial issue or an attempt to exploit a loophole. The purpose of the requirement to lay an SI before Parliament is so that speed measuring devices are subject to proper scrutiny.

"Those authorised since 1992 include laser speed meters, some types of which have repeatedly caused concern they can give false high readings. Had the proper procedure been followed, these devices might not have been authorised and drivers wrongly convicted."

The man behind the challenge is controversial Scottish lawyer Robbie the Pict, a man who won a battle to overturn toll charges on the new Skye bridge, and who has declared his own land on the island an independent country.

He and barrister Michael Shrimpton are pursuing several cases in both England and Scotland, and a test case is expected to go before the Court of Appeal soon.

A spokesman for the Home Office said: "This is an old chestnut that is brought up occasionally by the anti-speed camera lobby, but it has no basis in legality. The issue is a complex one, but it is simply not the case that modern speed cameras have to be individually sanctioned by Parliament, and all the correct procedures were undertaken to introduce speed camera technology to Britain's roads."