The government has rejected calls to limit powers that would allow magistrates to detain people who are thought to be 'contaminated'.

The measures, in the Health and Social Care Bill, are a response to incidents such as the murder of Russian spy Alexander Litvinenko from radiation poisoning in 2006.

In a letter to Andrew Dismore MP (Lab), chairman of the joint committee on human rights, which last week raised fears about the bill, health minister Ben Bradshaw wrote: "The government needs... the appropriate legislative tools to deal with public health threats."

The committee wanted the bill, which moved to the committee stage of the Lords on Monday, to specify the powers could only be used as a last resort, but Mr Bradshaw said sometimes measures would have to be put in place quickly.

Under the powers, people could be detained for up to 28 days, have property seized and destroyed and be prevented from working in order to prevent spread of contamination.

Another contentious issue in the bill is whether publicly funded residents of private care homes should be covered by the Human Rights Act.