The Home Office has conceded that the cost of its identity cards policy will be almost double its original estimate of £3 billion.

A revised cost-benefit analysis released alongside the ID Cards Bill yesterday put the projected cost to the taxpayer at £5.5 billion.

But the prime minister personally backed the plans.

"This is responsible government, not, as some have called it, Big Brother government," he said.

It was also revealed that those who refuse to register with ID cards database will be fined £2,500.