Which sector of the UK economy employs around 15 million people, creates at least as much economic value as the energy sector and yet contributes not one pound to measured gross domestic product? The answer is the volunteering sector. It may be one of society’s best-kept secrets. Let me lift the lid a little on this buried treasure.

There is no perfect way of measuring the size and contribution of the volunteering sector. Let me build up a picture starting with numbers of people, then working out how much economic value they create, before adding in some of the broader benefits of volunteering, either to the volunteer themselves or to wider society.