Lord Grade, chair of the Fundraising Regulator, has said the watchdog is looking into "about half a dozen or so" complaints that might warrant formal investigation.
Speaking on BBC Radio 4’s You and Yours programme yesterday, Grade said the regulator had received more than 300 complaints since it was launched in July.
Grade was being interviewed after the regulator published its first adjudication report, which was into what he called the "absolutely shocking story" of the now defunct agency Neet Feet.
The regulator found that seven major charities, including Save the Children, Unicef and the RNIB, had breached the Code of Fundraising Practice by failing to adequately monitor the work of Neet Feet, which went into voluntary liquidation in the summer after being the subject of an undercover investigation by The Sun newspaper.
Grade said the charities named in the report would be damaged by the negative publicity surrounding the case and the regulator would be monitoring them to ensure they had adequately improved their monitoring practices when working with agencies.
He told listeners he was pleased that so many people had been able to make complaints to his organisation because it had not done much publicity to inform the public of its role.
"We’re pleased that people understand there is an easy reference point for complaints from donors," Grade said.
He said that of the complaints it had received so far, many were settled by the charities themselves, but there were "about half a dozen or so that are serious enough for us to go into investigation".
Grade did not name any organisations that might face investigation. A spokesman for the regulator subsequently said it would not be revealing the names of those involved.
Grade said there were some very good fundraising agencies out there, but also some "cowboys" that needed close monitoring by charities that used them.