The Democratic Audit of the United Kingdom reports:

...there is growing evidence that the UK's political parties are a weak link in the chain connecting civil society to political decision-making. The three main parties certainly cannot claim to constitute mass membership organisations, embedded in and reflective of civil society. As figure 3 shows, the estimated membership of all three main parties has fallen substantially since the mid-1960s. Whereas they could once claim to have over 3 million members between them, the combined membership of the three main parties now amounts to a little over 400,000.

And:

The decline in turnout and party membership highlighted above suggest some serious grounds for concern - pointing to clear evidence of disengagement from the formal processes of representative democracy.

Source: http://www.democraticaudit.com/key-indicators-of-uk-democracy

Former UK Ambassador Craig Murray comments:

There is one constituent of a genuine democracy that the report does not seek to measure, but which I think could usefully be quantified by political scientists. That is the degree of real choice being offered by the political parties. I am sure that this has very substantially declined as well. There is no real choice on offer nowadays between the various neo-con parties. The differences on the timing and depth of cuts in public services, on continued privatisation of health services, on Trident nuclear weapons, on Afghanistan, on the money men who control the politicians, are miniscule. Only in Scotland do voters have a genuine choice of a different direction, and they take it.

This is a direct consequence of the other trends the Democratic Audit does measure. They show that the parties are more than ever, and constantly more, not avenues for popular participation but the domain of a political class and controlled by a wealthy “elite”. It is no wonder that they all have the same programme of promoting the interests of that elite.

Source: http://www.craigmurray.org.uk/archives/2012/07/29431/

Also:

Democracy in the UK has become almost meaningless. A monopoly of effective news flow by a deeply corrupt corporate media has crystallised the major party structures as the only real choices in the consciousness of the vast majority of voters. Those major parties have been so bought up by those same corporate interests that there is no genuine choice of policy on offer. If you were against the handing of untold billions of your money to the bankers, or the interminable and pointless Afghan War, you were one of a very large percentage of the population but had no mainstream party which respected, let alone represented, your view.

Source: http://www.craigmurray.org.uk/archives/2012/07/the-impossibility-of-rest/