You're being exploited in more ways than you know. The TUC reports, not for the first time and surely not for the last, on a form of exploitation that rarely gets attention in the media. Workers are contributing £29bn worth of free labour to British employers every year simply by working unpaid overtime. This surplus is being squeezed out of workers through market discipline – the threat of unemployment or reduced prospects.

Employees will be used to the expectation that they demonstrate "flexibility" in working beyond their core hours. This requirement is foregrounded in job interviews and reinforced on a daily basis, the term "flexibility" implying that this unpaid tribute is a personality trait rather than a structural facet of today's labour market. Workers are often expected to sign a "working time" opt-out that excludes them from protection under the law from having to work longer than 48 hours a week. The result is that 4 million workers regularly work beyond the 48-hour barrier, while past government research has shown that one in six workers actually workers longer than 60 hours a week. It gets worse. The average person's commute is equivalent to 139 hours per year, approximately four working weeks.

The huge burden of unpaid labour is the fruit of a long-term trend. In 1988, a quarter of male employees worked unpaid overtime. By 1998, it had reached 41%. The rise for female employees is even more dramatic, increasing from 25% to 58%. The difference is in part due to different occupations inhabited by men and women – the TUC points out that public sector workers, who are disproportionately female, are more likely to be performing unpaid overtime.

Moreover, this is one aspect of a general lengthening of the working week that has taken place over the last generation or so. Officially, the statistics show a sharp decrease in the number of people working long hours since 1998. These sorts of statistics have been used by the government to justify continued opt-outs of working time directives, since they argue that the goal of reducing long working hours is being reached in practice. In fact, what the statistics really disclose is the increasing casualisation of work, registering a huge increase in part-time jobs.

The average working week for full-time employees is approximately 42 hours in the UK, above the EU average and certainly well above countries which retain comparatively strong welfare systems such as France or Denmark. The UK tends to be closer to extreme neoliberal economies created in the east of Europe after the collapse of the USSR than to relatively social democratic economies in the west of Europe.

The irony is that while working longer hours than a generation ago, and working more unpaid labour, we are getting less as a share of national income for our trouble. As a share of GDP, wages have fallen from a high of 64% in 1974 to approximately 54% in 2010. This is despite the fact that we have become more productive. A 23-hour working week in 2003 was equivalent in productivity to a 40-hour working week in 1975. There is a growing gap between productivity and wages, and the richest are creaming off a growing share of all new growth. And it promises to get no better. Mervyn King recently admitted that average wages are likely to be no higher in 2011 than they were in 2005. This may partly be explained by the fact that between mid-2009 and early 2010, 89% of all new income had gone to profits. In truth, £29bn (this year) is only a fraction of the total surplus that is being extracted from workers.

Amid a certain fashionable revival of Marx in some corners, it shouldn't be controversial to call this for what it is: a stark increase in the rate of exploitation. What has happened is the direct culmination of Thatcherite class war, aimed at breaking up the bargaining power of labour in order to restore profitability to what was a crisis-hit British capitalism. Today, capitalism's crisis is all the deeper, and thus the official remedies are all the more catastrophic. On the basis of past experience, the likely result of the Tory-led government's war on the public sector and the last major bastion of trade union strength, should it prove successful, will be to further strengthen the disciplinary whip of the market, compelling fewer people to work more for less.

Meanwhile, workers interested in retrieving some of the loot exacted from them might consider the example of workers in Mahalla and Suez who have demonstrated that militancy can withstand military dictatorship as well as army diktat. British workers are in a much stronger position, and their opponent is much weaker.