The head of the Charity Commission has warned charities not to "hound" people for money as he sets out plans to recover the scandal-hit sector's reputation.
William Shawcross said public trust in charities has taken a major hit in the wake of a series of scandals which have left the public feeling some organisations have let their "values be obscured".
And he warned it is not acceptable for charities to aggressively pursue the elderly, vulnerable and generous for money through letters, nuisance calls and street fundraisers known as "chuggers".
Last May, great-grandmother and poppy seller Olive Cooke, 92, from Fishponds in Bristol, killed herself after reportedly receiving hundreds of letters from charities asking for money.
Just three months later Kids Company collapsed amid allegations of financial mismanagement, and earlier this month an investigation by The Sun revealed Age UK made £6 million from energy giant E.ON for recommending a tariff which was not the cheapest on the market.
Mr Shawcross told a meeting in Southampton on Monday: "We have set out more clearly than ever what trustees must do to ensure their fundraising practice fits with the values which accompany charitable status.
"Simply put, it cannot be right for vulnerable people, older people, generous people, to be hounded, on the telephone, through the letter box or in the street."
He told the audience of charity figures that the "tragic case" of Mrs Cooke and "awful" collapse of Kids Company has thrust charities into the spotlight and poor practice by a few "bad eggs" has been uncovered.
Mr Shawcross added: "But even without specific scandals, there has been a feeling that the practice in some charities has strayed from their guiding values.
"Now some have blamed the media, but this is to miss the point. The impact of revelations of the last year have been felt so strongly because they struck a chord with the public.
"The stories found a receptive audience who thought in recent years that perhaps some charities had allowed their values to become obscured as they adopted the sharp practices of industry."
He said a new charity fundraising regulator is being set up in the wake of claims about Mrs Cooke and bullying fundraising tactics among some charities.
This is the "last chance" for the sector to prove it can regulate its own funding, otherwise the Charity Commission might be asked to step in, he warned.
The Charity Commission is issuing an alert to trustees at all 1,700 charities demanding they review their commercial relationships.
The regulator says that while it is legitimate for charities to have commercial partnerships to help them fundraise, trustees must be careful to protect the reputation of their organisation.
Charities must check for conflicts of interest, ensure partnerships are properly documented and reviewed regularly, and that the commercial benefits to the charity are made clear, it said.
Those who fail to comply will be subject to regulator action, the Commission warned.
Mr Shawcross also announced that larger charities may be asked to contribute to the funding of the Commission after its budget was slashed by 50%.