What does my employer mean when they say my working time is 'unmeasured'?

The definition of partly unmeasured working time (unpaid overtime) has been clarified as the result of a European Court of Justice decision in 2006,

The definition of 'unmeasured working time' is still a bit vague, but is intended to apply to senior managers and executives who genuinely have control over their own working time. These workers are entitled to paid holidays but don't receive other working time rights. Workers who are free to set their own hours are deemed competent to look after themselves and are thus exempt from the working time limits and rest break provisions.

The problem is that many managers in long hours workplaces still behave as though this exemption also applies to all white-collar workers, for the so-called 'voluntary' work they 'choose' to put in over and above the hours specified in their contract (and for which they aren't paid). Many managers are not yet aware that the law in this area has changed in 2006. You should take further advice if you are concerned about unpaid overtime.