The Charity Commission will embark on a new set of public benefit assessments later in the year.
The exercise will involve an as yet undetermined number of small charities, fee-charging charities other than schools and care homes, and charities for which the rule that any private benefits must be incidental "may be an issue".
The announcement follows the release last week of the results of the commission's first round of public benefit assessments. The regulator held that four of the 12 charities it assessed did not generate sufficient public benefit.
St Anselm's School, Highfield Priory School and Penylan House Jewish retirement and nursing home were all deemed to be doing too little to make their benefit available to people who could not afford their high fees.
The regulator said it was unable to assess the public benefit of The Rest, a convalescent hotel in Wales, because it was acting outside its objects. The four religious charities assessed all passed.
A spokeswoman for the commission said its next assessment programme would begin later in the year after a review of the costs and benefits of the first programme.
She said some small charities would be chosen so the commission could determine a proportionate public benefit requirement for them.
The regulator was keen to explore the principle that private benefits must be incidental, she said, but she was unable to give examples of the kinds of charity that might be looked at.
She said there would be further surveys and a study of charities' annual returns.