Bad volunteers are like a "cancer in your organisation", according to Stephen Peck, operations director at the Scout Association.
Peck, whose organisation has 120,000 volunteers, told delegates at the Charity Finance Group conference in London yesterday that problems most often arose when volunteers did not receive the level of management required.
"The biggest risk to your organisation is that you’ve had someone there for 30 years and they’re a pain," he said. "They annoy others or they’re rude to customers in your shop.
"We’ve all come across volunteers who are blockers. You get rid of them and lots of other people immediately offer to help. Those people are like a cancer in your organisation."
Peck said another major problem was when volunteers fell out. "When that happens, it’s often because they aren’t getting enough management support," he said.
He said charities should set up fixed terms of service for volunteers and not be afraid to tell them that their services were no longer needed.
Volunteers required and deserved the same quality of management as employees, he said. "One thing that’s important is clear role descriptions," he said. "Make sure volunteers are clear what’s expected of them.
"Have clear line management. Too many volunteers don’t know who their manager is.
"And don’t apologise for being thorough. Carry out background checks. Agree that you’ll have them in post for three, four or five years, maximum. At the end of that period, renew, retire or reassign."
Peck said that other common volunteer issues his organisation faced included complaints from parents, the threat of litigation and volunteers not following rules laid down for them.