There is a large pool of volunteers in the United Kingdom (around a third of the population) who volunteer at some stage during the year. At any point in time, however, there is a smaller, but stable, pool of 'active' volunteers. It is these active volunteers that are used in the HHSA project to estimate the number of unpaid voluntary hours that are undertaken by the population.

‘Active' volunteers undertake a range of voluntary activities. This work includes fundraising, clerical support, being a school governor, organising a scout group or providing a counselling service for a local self-help group. Nearly half (47 per cent) of the work undertaken by 'active' volunteers was of a clerical or secretarial nature, and 28 per cent of volunteering episodes involved activity which can be classified under the professional occupation heading. A quarter of episodes were spent in activities which could be classified as personal and protective occupations.