A cross party group of peers has challenged the government's mental health bill, with the Lords voting for a series of amendments that weaken the proposed act's power to detain people with severe personality disorders without consent.
The government's original bill would allow people deemed to be a threat to themselves or others to be detained for treatment against their will, even, critics claim, if it was not shown that such treatment would improve their condition.
Introduced by the Department of Health and Home Office, the government will now have to decide whether to contest the amendments when the bill moves to the Commons.
Critics warn that the legislation risks deterring people from coming forward for treatment. However, health minister Lord Warner has claimed that the bill protects public and patients from harm.
Peers from the Liberal Democrats and Conservatives claim they do not want the government to abandon the bill but are instead asking the government to accept a series of amendments, which the Lords are expected to vote on later today.
Chiefly, the amendments ensure that individuals can only be detained for treatment if there is a "likelihood" of the person benefiting from it. The government requires only that the "purpose" of treatment is to alleviate or maintain the disorder or symptoms. Critics claim that this creates the possibility that someone could be detained for preventive purposes.
The amendments also require that the decision to renew a detention order receives a similar degree of consideration as the original order. The peers maintain that deciding to renew a detention order is no less serious than sectioning an individual in the first place.
The Lords also demanded that the act would not allow someone to be detained solely on the basis of their orientation or identity, political, religious or cultural beliefs, disorderly conduct and substance abuse.
"This is a crucial factor in preventing the bill from being used inappropriately," the cross party peers warned, citing concerns that the bill represents an attempt by the government to broaden the definition of mental disorder.
The government first attempted to change the mental health laws in 1998, following Michael Stone's conviction for the murders of Lin and Megan Russell, after he was deemed a dangerous but untreatable psychopath.
The government last month defended the bill against critics in the Lords. Health minister Rosie Winterton said: "We have made it very clear in the bill that appropriate treatment has to be available for detention to take place."