If asked which groups posed the greatest threat to individual liberty in modern Britain, I would unhesitatingly cite two groups. These groups are, broadly, the medical profession and those who are generally called 'celebrities' - pop stars, film stars and so on. You may think that I am being somewhat tongue-in-cheek (and in some ways I am), yet there is a serious set of issues at stake here.
Firstly, the medical profession. Hardly a day goes by without some group of doctors or medical scientists calling for a ban on this or some sort of government intervention in that. The latest example seems to be the attempt to set a minimum price of alcohol sales, a terrible idea  which, hopefully, has failed. Consumption of tobacco, salt, sugar, fat plus associated advertising are all deemed dangerous and suitable subjects for medics to attempt to ban or circumscribe via price increases . Medics also see fit to spend public money to instruct us how to live our lives and what choices we ought to make.
Some of the rationale for this comes from the doctor's protective monopoly, the NHS. As the health costs of unhealthy lifestyles are born by the state, it seems quite justified for doctors to call for bans and price hikes. Naturally, this simply demonstrates the lunatic incentive structure that state-provision of healthcare creates, especially free-at-the-point-of-delivery healthcare which externalises the costs of unhealthy behaviour. However, the chief threat from doctors lobbying stems from their apparently impartial and expert position as guardians of health and security. Unfortunately, most of their calls ignore the Public Choice and Knowledge Problem implications of the state interventions which result.
Celebrities have an even less programmatic threat to liberty, unsurprisingly for such a diverse group. They usually adopt a single-issue approach. For a long time we have had Bob Geldof and Bono calling for state spending on international aid. The greatest current threat stems from Hacked Off's campaign against a free press. Celebrities will often lead opposition to reductions in public spending or state activity such as Arts Funding. They have a powerful ability to rally strong public opinion for or against a cause, no matter how strong the case against - whilst Joanna Lumley's campaign to allow Gurkha's to settle in the UK hardly represents a major threat to liberty, although it has had some unintended consequences for Aldershot, it serves to demonstrate the power without responsibility that celebrities wield.
In distinction to the recent past, where ideological opponents of liberty tended to possess a coherent ideological programme of state intervention and control, these groups are far more pragmatic and opportunistic. Thus, in many ways, they are far more dangerous because they cannot be so easily shown to be a threat. It must be said that both groups 'mean well' - they cannot really be accused of a malign plot to oppress people. However, both represent a serious threat to liberty.
Regulations and public spending, once in place, are rarely repealed and tend to expand as they crowd out private responses. Innovation is prevented and alternative solutions are foregone. Bans and prohibitions create black markets and often serve to create other problems without solving the first (viz. recreational drugs). Whilst everyone has a right to free speech, those lobbying for state intervention need to be aware of the consequences and problems created by their support for the insidious expansion of the state into yet more aspects of our lives.