The UK government's plans to introduce lie detector tests for benefit claimants have sparked a storm of controversy.

Under proposals announced by the Department for Work and Pensions, benefit claimants would be assessed during phone calls by software that claims to be able to tell if they are lying about their status.

The government said that a positive result will spark an investigation. But the plans have drawn sharp criticism from opposition parties and unions.

"This sounds like yet another government gimmick which we suspect will be used in only a tiny minority of cases," said Liberal Democrat Shadow Work and Pensions Secretary David Laws.

"If the government really wants to reduce the amount of fraud in the system it must tackle the complexity of benefits such as tax and pension credits.

"It must also introduce common sense measures, such as cross-checking other benefit claims, which have often been ignored."

The TUC claimed that the problem with the lie detection technology that the Department for Work and Pensions intends to use is that it cannot detect lies.

Voice risk analysis and lie detectors can only detect, with varying accuracy, changes in the body, such as heart or breathing rate, or any changes in the tone, pitch or tremors in the voice.

TUC General Secretary Brendan Barber said: "Ministers should think again and abandon plans to subject benefit claimants to untested lie detector technology.

"Unfortunately, people for whom deception is a way of life tend to pass lie detector tests with flying colours while the scrupulously honest often fail.

"If people know that their voices are to be analysed for every blip and tremor, the danger is that genuine claimants will be intimidated into withdraw ing their claims, or will have to wait ages for their money while they provide extra evidence."