A court is due to rule on a legal test case which could pave the way for an avalanche of challenges to speed camera convictions from millions of motorists.
Lawyers are arguing at Manchester Crown Court that all devices authorised since 1992 are illegal because the law introducing them on to British roads had been wrongly implemented by successive home secretaries.
A successful appeal on the constitutional principle may lead to drivers demanding repayment of an estimated £600 million in fines imposed and the annulment of penalty points and bans.
Retired computer engineer Aitken Brotherston, 61, of Lymm, Cheshire, has brought the case on appeal against his conviction for driving 52mph in a 40mph zone.
Mr Brotherston said he "firmly believed" that the LTI 20/20 Speedscope laser gun which captured his speed provided an inaccurate reading.
Defence barrister Michael Shrimpton said each home secretary since Michael Howard had effectively set up their own scheme of ministerial approval and were wrong to pass such devices as the LTI 20/20 without parliamentary scrutiny.
Mr Shrimpton said the case concerned a "big constitutional point" which addressed the "fundamental relationship between the executive, the courts and the legislature".
He said there was no problem with lasers as a precise speed measurement but the way in which they were operated, which Parliament should have the opportunity to debate.
He added it was "horribly unconstitutional" for ministers to evade parliamentary scrutiny with general orders which did not specify devices.
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A number of cases throughout the UK similar to Mr Brotherston's are currently in the court system which Mr Shrimpton said was likely to be eventually resolved in the House of Lords.
