In China it is commonplace for individuals who challenge state officials to be committed to psychiatric institutions where they may be held indefinitely (http://www.guardian.co.uk/world/2010/aug/31/china-mental-hospital-liao-meizhi). We run the risk of similar practices arising in the UK with the establishment of such sinister organisations as the Fixated Threat Assessment Centre, that uses police psychiatrists to identify individuals who may pose a danger to high profile public figures.
This is a particularly important issue given that such practices (i.e. MHA sectioning) are being used to deal with terrorism suspects and that the legal definition of terrorism is so broad ranging. We need to ensure function creep does not allow psychiatry to be used as a means to silence political disidence, be that through actual inappropriate application of mental health laws or by creating a culture in which people are reluctant to speak out because they fear the consequences (including possible detrimental effect on future career and financial prospects).
I do not believe we have adequate safeguards against this in the UK and that must change.