The voluntary sector has taken its eye off the ball by cultivating relationships with government rather than business, according to the NCVO.
Campbell Robb, director of public policy at the NCVO, said charities could influence ministers more with corporate backing than they could on their own.
"The corporates bring influence we can't even dream of to places we can't even get to," he told NCVO's corporate community involvement seminar last week. "When we go to the Treasury and they see we have two-thirds of the banks behind us, that sways them."
Martin Mosley, consumer and community affairs director at Barclays, said: "We have no difficulty in getting access to the Chancellor." He added: "We would like to bring skills back to the third sector, but not in an arrogant way."
However, Mosley warned that he could only engage with charities if they had a dedicated account manager who spoke the same business language.