Statute Law Database
The Statute Law Database, a free database of revised UK primary legislation, was launched on 20/12/06. It contains primary legislation that was in force at 1/2/91 and primary and secondary legislation that has been produced since that date. The primary legislation has been revised to 2002 and half is fully up-to-date. All secondary legislation is shown on the Statute Law Database as originally published, unamended. See the judicial comments in R v William Chambers  EWCA Crim 2467 for unfortunate consequences of the difficulty in finding out what the law is.
Unfortunately, few Acts relating to mental health law have been updated beyond 2002. To compensate for this, you must check the Tables of legislative effects for recent updates to each Act. Note that not all the updates listed in these tables are in force, so you will need to search through the relevant commencement orders. Also, there can be a fortnight's delay before updating legislation is added to the website or the tables of legislative effects. This updating process has been gone through for the legislation reproduced on Mental Health Law Online on the date specified in the relevant index page of this site.