The government’s Giving Summit in May is "in danger" unless the government withdraws a proposed cap on tax relief for major donors, charity representatives have warned.
The cap, announced in the Budget, will mean that tax relief an individual can claim in any year will be limited to a quarter of their income or £50,000, whichever is higher, from April 2013.
This will affect higher rate tax relief and Gift Aid, gifts of land and shares, and payroll giving, and could make it more expensive to give more than £100,000 to charity.
It is likely to impact most heavily on those giving the most to charity, particularly anyone who donates a one-off windfall.
The summit, which is to be held on 8 May, is intended to address issues preventing philanthropy, but voluntary sector leaders said the new cap would overshadow all of those concerns.
"If this is not sorted out, then the Giving Summit is in danger," Sir Stephen Bubb, head of the chief executives body Acevo, told Third Sector.
"Voluntary sector leaders won’t want to sit through an event celebrating the first anniversary of the Giving White Paper if their fundraising has just been hit through this silly and ill-thought-through measure.
"I’m not sure the Treasury fully understands the impact this will have on the government’s wider philanthropy agenda.
"We’re hoping with persuasion they will exempt charitable giving from this new measure, which is what they should have done in the first place."
Karl Wilding, head of research at the National Council for Voluntary Organisations, said: "This is probably going to be the major topic of conversation at the Giving Summit in May, unless the government announces changes between now and then.
"This runs totally contrary to the government’s message that it wants to build a culture of philanthropy in this country.
"It’s just introduced something that could massively harm that culture."
Beth Breeze, a researcher in philanthropy at the University of Kent, said she thought no one would pay attention to the supposed topics at the summit.
"I’m supposed to be chairing a session on the perception of philanthropy in the media," she said. "That’s worthwhile and important. But who’s going to care about that if we’re debating this cap and what it will mean for charities?"