Campaigners remain "deeply concerned" that people subject to compulsory powers under the Mental Health Act 2007 will miss out on an advocacy service to be launched next week.
Mind's policy and campaigns manager Anna Bird said service users could be waiting "many more months" after the 1 April deadline before fully trained advocates are available in some parts of England.
Patients subject to community treatment orders and detentions under the act, which came into effect in November 2008, are legally entitled to independent mental health advocates (IMHAs).
However, Bird said services had been left with "very little time" to prepare after primary care trusts were only awarded commissioning responsibilities in December.
Charles Walker, Conservative MP for Broxbourne in Hertfordshire, who served on the parliamentary committee that scrutinised the act, said: "Sufficient progress is clearly not being made to provide the mentally ill with qualified advocates. It is simply not acceptable to deny people representation when their liberty is at stake."
A Department of Health spokesperson said the roll-out of IMHA services had been supported by the National Institute for Mental Health in England.
"Local services have been aware for a number of months that the provisions on IMHA services would be introduced from April 2009," the spokesperson added.
Roll-out of mental health advocates may be delayed
Expert guide to Mental Health Act