The cost of introducing national identity cards could rise to well over £100 a person if Labour meets a commitment to offer discounts for those on low incomes and the elderly, according to internal Home Office estimates.

Charles Clarke, the home secretary, is understood to be trying to contain the rising cost of the ID card scheme in the face of growing unease among Labour backbenchers. He is looking at a faster roll-out of the scheme, but may need to find savings if this pushes the cost up even further.