The Lloyds TSB Foundation for England and Wales carried out the survey, which sought the views of more than 650 small to medium-sized charitable organisations.
The survey, published this month, found that 56 per cent of charities had seen an increase in interest shown in volunteering opportunities. But 28 per cent of them said they were unable to respond adequately to this surge in interest because of resource and budget limitations.
Linda Kelly, chief executive of the Lloyds TSB Foundation, said the true cost of unpaid staff was often overlooked.
"These results reflect the fact that volunteering is not ‘free’, and although volunteers may themselves be unpaid, they still require support, training and expenses so they can assist their organisations to the fullest extent."
The survey also found that 85 per cent of charities had experienced a rise in demand for their services among users, with 44 per cent saying the increased pressure on their resources was making it harder to meet these needs.Seventy-seven per cent of respondents said that the existing levels of assistance from central and local government for charities were inadequate.