The government's focus on public safety is 'key' to a sharp rise in the number of mental health patients sectioned in the past two years, say policy experts.

The number of patients formally admitted without their consent has jumped by 4,000 in the past two years, to 27,100. A decade ago, 16,000 patients were sectioned under the 1983 Mental Health Act.

Mental health experts believe political pressure has led clinicians to lower the threshold at which patients are judged to require sectioning.

Edward Peck, director of the Centre for Mental Health Services Development, said: 'One of the issues is that assessments of risk are not a precise science. Clinical judgements will be influenced by the political environment. . .

'In the aftermath of the Michael Stone case I am not really surprised that clinicians are being more cautious.' Stone's conviction last year for the murder of Lin and Megan Russell sparked a debate over the treatment of mentally ill and peronality-disordered patients.

Solicitor Peter Edwards, director of the Institute of Mental Health Law, said it was 'impossible to prove' a link between the rise and a government strategy of, 'if in doubt, section them', because of confounding factors surrounding the 'Bournewood' case.

In December 1997, the Court of Appeal ruled that consent to admission could not be assumed in the case of patients judged 'incapable' to give it.

In July 1998 the House of Lords distinguished between those patients objecting to treatment, for whom a formal section would be required, and those who had made no objection, for whom consent could be assumed.

But since then figures continue to show a rise in patients sectioned - with an increase of 2,000 patients in 1998-99.

Dr Matt Muijen, director of the Sainsbury Centre for Mental Health, said a shortage of beds meant some patients were not admitted until their symptoms became extreme - and hence less likely to be admitted voluntarily.

But he said the emphasis on risk meant that other patients perceived to be 'dangerous' - although presenting fewer symptoms - were likely to be sectioned earlier.

Statistics on Formal Admissions Under the Mental Health Act 1983.