William Shawcross, the chair of the Charity Commission, should resign because his views and prejudices bring his office into disrepute, the chief executive of the Scottish Council for Voluntary Organisations has said.

Martin Sime (pictured) wrote an open letter to the chair, after Shawcross gave a wide-ranging interview with The Times in which he criticised Oxfam and the RSPCA – saying the latter’s trustees were "militant" and some of its actions "grotesque". He suggested that he favoured banning door-to-door fundraising, and expressed a willingness for the Commission to regulate fundraising in the sector.

Shawcross also criticised charities over the death of Olive Cooke and said that charitable funds were being diverted to terrorism.

The Charity Commission does not have direct jurisdiction in Scotland, where charities are regulated by OSCR, the Scottish Charity Regulator. But Sime said he still felt Scottish charities would be affected, because the “irresponsible and negative consequences” of Shawcross’s remarks would be felt throughout the UK.

Sime wrote that Shawcross’s views suggested he was not “an individual who is capable of conducting the affairs of the Charity Commission in a fair and impartial matter”.

The letter in full reads:

"I write following reported remarks that you made to The Times newspaper which were published on Saturday 1 August 2015.

"Quite simply, I believe that the views you hold and the prejudices which you reveal bring the office you are appointed to into disrepute, and that you should resign from the position of Chair of the Charity Commission forthwith.

"As you are well aware, the Charity Commission is not responsible for the regulation of charities in Scotland. Your comments as reported, however, go way beyond any interpretation of individual national regulatory frameworks, and seem designed to undermine public trust and confidence in charities wherever they are located.

"Whilst you are not directly responsible for a general failure in the media to convey the geographical limitations of your remit, the irresponsible and negative consequences of what you have said will be clearly felt by the public, by members of SCVO, and by charities throughout the UK.

"I find it inconceivable that you should cast aspersions on the strategies and workings of individual organisations which have broken no rules or committed any crimes. Your rehash of various scare stories which are characterised by a lack of evidence, and the utterly false conclusions you draw from one reported incidence of fundraising abuse, do not speak of an individual who is capable of conducting the affairs of the Charity Commission in a fair and impartial matter.

"It would be completely wrong of you to suggest in any response that I am trying to draw attention away from bad practice in the charity sector. We face significant challenges to our accountability and legitimacy on a daily basis because all of our work is underpinned by public trust and confidence. That is precisely what makes your recent intervention inexcusable."

Shawcross said he was surprised at the tone of the letter and that he will reply in due course.