Serious questions were raised last night about the First Minister's assurance that no patients would be moved from Scotland's top security hospital without ministerial approval.

Alex Salmond's claim, made in parliament on Thursday, followed the revelation in The Herald that almost half of the patients at the State Hospital in Carstairs are to be transferred to lower security units.

However, legal experts accused Mr Salmond of being "economical with the truth" and Labour and Conservative politicians said he had "misdirected" parliament.

Mr Salmond told MSPs that "any transfer of a restricted prisoner and resident at Carstairs requires ministerial approval".

However, under the Mental Health (Care and Treatment) Act 2003, patients have the right to appeal against "compulsory measures" and being held in "excessive security".

The tribunal decides on whether the level of security is appropriate but in the case of restricted patients the First Minister has to consent that the receiving hospital is appropriate. Ministers can give reports to the tribunal stating their opinion of where a restricted patient should be held and can appeal against decisions they disagree with.

The Scottish Government last night insisted that Mr Salmond was correct.

The move to cut the number of beds in the State Hospital from 240 to 140 by 2011 follows concerns that, under the European Convention on Human Rights, patients kept in an "excessive" level of security could sue the government.