British charities face desertion by a large part of their voluntary workforce unless they urgently adapt, according to an independent commission.

In a paper entitled A Better Offer, published today, the Independent Commission on the Voluntary Sector and Ageing warns charities to improve the way they work with “super boomer” volunteers - the most qualified members of the generation now in their 50s and 60s.

The commission is supported by think tanks New Philanthropy Capital (NPC) and ILC-UK, and has been set up to assess how the sector needs to adapt to an ageing population.

The report says "super boomers" will face later retirement and greater childcare responsibilities of grandchildren at an older age. It says the time available to help charities will significantly reduce unless charities can make a more compelling offer to potential volunteers.

As a result, it says, charities must create more flexible placements, must more effectively explain the benefits of volunteering to older people, and must ensure volunteers do not feel exploited and taken for granted. It also recommends introducing specific measures to appeal to men, who are currently less likely to volunteer.

Volunteering by older people is currently valued at £10bn a year, the report says, and is estimated to grow to £15bn by 2020 as Britain’s population grows larger and older.

Dan Corry, chief executive of think tank New Philanthropy Capital and a member of the independent commission (pictured), said: “Older people have traditionally volunteered for charities in their droves. Without the massed ranks of retirees who stuff envelopes and take minutes in meetings, thousands of charities would struggle to survive."

He said charities needed to act now to ensure they kept volunteers' support.

“If we get this right the future looks rosy, but get it wrong, and act too late, and there’s a real risk that charities will find their volunteer army heading for the hills," he said.

"Older volunteers are among the most generous volunteers, giving thousands of hours to causes they care for, often in menial tasks and with relatively little in return. But charities are naïve if they think that the next generation will put up with the same thing.”

A total of around 23m people from across the generations, volunteered in England in 2012, with a total estimated value of £24bn to charities each year.