The rights of millions of British motorists are at stake in a legal battle brought to Europe by campaigners against speeding laws.
Human Rights judges in Strasbourg are hearing a complaint that forcing car owners to state who was behind the wheel of a vehicle caught speeding on camera breaches their right to silence.
The British government said it would "vigorously" defend current motoring rules - but if drivers Idris Francis and Gerard O'Halloran win their claim it could curb the Department of Transport's money-raising ability through speeding fines.
The campaign group Liberty is backing the two motorists, who turned to the Human Rights court when their objections were dismissed in domestic courts.
Mr Francis, from West Meon, Hampshire, refused to say who was at the wheel of his vintage Alvis when it was photographed in Surrey breaking the 30mph speed limit.
He said forcing him to provide evidence of the alleged offence breached his right not to incriminate himself.
Similarly, Mr O'Halloran, from London, objected because he said he faced a fine for not revealing who was at the wheel of his car when it was photographed speeding in Essex.
Paul Smith, founder of the Safe Speed road safety campaign said: "Despite rapidly mounting evidence that speed cameras have proved to be a deadly mistake, government appears to be incapable of seeing the damage that's being done."
He went on: "The so-called 'right to silence' is ancient and worthy. I am certain that speed cameras have made our roads considerably more dangerous by diverting attention from more important safety factors."
A Department of Transport spokesman said: "The UK Government does not accept this claim and is vigorously defending this case. We are confident of its defence, which has been upheld in the UK courts."