The definition of 'unemployed' for ONS is anyone
"1. without a job, have been actively seeking work in the past four weeks and are available to start work in the next two weeks, or
- out of work, have found a job and are waiting to start it in the next two weeks"
They also measure people who are 'economically inactive' and fall outside this definition. As at May 2012 40,193 m people were aged between16 and 64. Of those 9,207 were economically inactive ... ie. in full-time education or otherwise not working but not actively seeking work. The rate of economic inactivity was 22.9% in May and 23.1% in February... so also coming down.
You should check out the ONS website. Mine of information.