The number of charity shops has expanded dramatically over the past 15 years, with Oxfam alone now equivalent in size to the Dixons electrical chain. But this expansion, and increasing competition for staff, has led to a crisis in attracting volunteers.
Avril Maddrell of Westminster College, Oxford, has been investigating the place of charity shops in the retail sector, with the help of Suzanne Horne, of Stirling University's marketing department.
She told delegates at the geographers' annual conference: "Ten years ago, charity shops weren't considered very attractive places to go, often characterised by a rather run-down appearance and associated with the musty smell of jumble sales.
"But the sector has been professionalised and accommodation is increasingly being transformed into good shopping environments, with large 'chains' like Sue Ryder using a brand image with uniform shop frontages."
But while the number of shops has grown, they are finding it difficult to find a supply of reliable volunteers. Estimates of the number of charity shop volunteers range from 50,000 to 200,000, and while volunteering in general is split fairly evenly between men and women, more than 90 per cent of charity shop staff are female.
"In the past, there were more women to be drawn on once their children were of school age, but now many of these women are going into paid work and are not available," said Dr Maddrell.
Difficulties also stem from the trend for charities to decide centrally rather than locally to set up a shop. The research team found that managers of shops that are firmly grounded in the community are more likely to have a reserve of volunteers. One Isle of Man manager said: "In a place like this, if you're short, you just ask your friends in the Women's Institute and they come and help."
But shops are now finding innovative ways of widening the pool of volunteers, often by "fostering interesting community links", said Dr Maddrell.
These include sixth-formers completing the community service element of the Duke of Edinburgh Award scheme, who can provide summer holiday cover; and social work referrals of people who have difficulty finding paid employment because of physical disability, mental health problems or low self-esteem.
Some shops are taking on community service workers, commonly people who have committed driving offences, who often prefer back room work such as sorting and steaming clothes.
Dr Maddrell said: "I think this could become more prevalent as people's attitudes to community service become more positive. These people are paying something back to the community in a positive way and they're not taking a job away from anyone.
"This links to their broader social mission which for many is not just about raising money, but serving the local community."