'The best measure of union power is the union density figures... The level of density approximates the level of power because the higher the proportion of the workforce that is represented, the more influence we are seen to have’ writes Michael Crosby in his book ‘Power at Work’.
The TUC’s Stronger Unions blog reports that the Department for Business Innovation and Skills (BIS) has published its annual report on Trade Union Membership and that union density is 26.6% of employees (14.2% in the private sector and 56.3% in the public sector) :
http://www.strongerunions.org/2011/05/03/trade-union-membership-2010/
Although these figures mark a very slight reduction in (already low) union density levels, collective bargaining coverage is falling at a faster rate - now standing at 30.8% of all employees (16.8% in the private sector and 64.5% in the public sector) down from 32.7% in 2009 which represents a decline of 6% in one year.
The latter reflects not just a withdrawal of industry wide agreements but the reality that most employment growth is taking place in the non unionised services sector:
The full and highly informative BIS report is available here: http://stats.bis.gov.uk/UKSA/tu/sa20110428.htm