Sir Stephen Bubb, chief executive of the charity leaders group Acevo, has written to George Osborne, the Chancellor of the Exchequer, asking whether claims that it plans to slash £320m from the budget of the Big Lottery Fund are true.
The claims were made last week in a blog by a group calling itself Save Big Lottery and publicised on Twitter.
The blog said the group had been told by "reliable sources" that in its Comprehensive Spending Review, to be unveiled on 25 November, the government planned to redirect £320m of the proceeds the BLF receives from the National Lottery.
It said the money would instead be used to fund the arts, heritage and sport, making up for budget cuts at the Department for Culture, Media and Sport. Based on the £670m of good cause funding the BLF received last year, this would represent a 48 per cent cut.
It is not clear who is behind the blog.
Acevo declined to share the full contents of Bubb’s letter, but a spokesman for the chief executives body said: "The letter sought clarification on the substance or status of the rumour and pointed out the value and significance of the contributions made by the BLF to charities and good causes.
"It underlines the value and the contribution the BLF makes to small and large charities as well as long-term, structural causes, such as the ageing population."
Last week, charity groups including Acevo, the Directory of Social Change and the local infrastructure body Navca called the claims outrageous and disgraceful, and warned they could have drastic consequences if true.
A Treasury spokesman previously told Third Sector it would not comment on speculation.