Patrick Cox, founder and chief executive of the Small Charities Coalition, has left the organisation.
Cox registered the coalition as a charity in January 2008 after his experiences in setting up the Male Cancer Awareness Campaign convinced him that small charities needed more support.
The coalition, which has 350 members and employs three staff, matches charities with incomes of less than £1m with large organisations that have skills they lack.
Cox upset his trustees in September when Third Sector printed an article about whether charities should accept donations from the British National Party.
In his capacity as chief executive of the coalition, he said "you have to have a good reason to turn money away, wherever it comes from. I don't think you can reject it because you might upset a few people.
"If it's just because you don't believe in their views, then I don't think that's good enough."
Speaking on behalf of the Male Cancer Awarness Campaign, he said it probably would accept a donation from the BNP.
Debra Allcock Tyler, who chairs the coalition, said afterwards "we would not, under any circumstances, accept a donation or gift from them".
Acting chief executive Cath Lee said Cox's departure was not linked to his comments.
"Patrick always intended to step down once the coalition was up and running," said Lee. "The pace of development at Male Cancer Awareness has increased recently, and he felt he needed to give it his full attention.
"The trustees and staff at the coalition are proud of what Patrick has achieved for the Small Charities Coalition and thank him for his vision, drive and determination over the past few years."
Lee said trustees would meet in the next few weeks to discuss finding a successor.
Cox, who left three weeks ago although his departure was only announced yesterday, said: "It's hard to leave your baby, but my first-born, the Male Cancer Awareness Campaign, was struggling. Things were just not getting done because there was no staff driving them.
"The coalition has gone from strength to strength and achieved huge success in a short time."