“Every government will do as much harm as it can and as much good as it must” was written by British journalist Claud Cockburn (1904-1981) in his autobiography A Discord of Trumpets (1956). The line is sometimes credited to British anarchist and atheist writer Nicolas Walter (1934-2000), but it’s probable that, if Walter did use it, he was simply borrowing Cockburn’s line.
 
   
Wikipedia: Claud Cockburn
Francis Claud Cockburn of Brook Lodge, Youghal, County Cork, Munster, Ireland (pron.: /ˈkoʊbərn/ koh-bərn; 12 April 1904 – 15 December 1981) was a British journalist. He was a well known proponent of communism. His saying, “believe nothing until it has been officially denied” is widely quoted in journalistic studies. He was the second cousin, once removed, of novelists Alec Waugh and Evelyn Waugh.
 
Google Books
London Charivari
Volume 226
1954
Pg. 555:
Take the charitable view, bearing in mind that every Government will do as much harm as it can and as much good as it must.
 
Google Books
A Discord of Trumpets:
An Autobiography
By Claud Cockburn
New York, NY: Simon and Schuster
1956
Pg. 204:
“One should perhaps avoid being hypercritical of acts of high policy. Take the charitable view, bearing in mind that every government will do as much harm as it can and as much good as it must.”
 
Google Books
Marxism Today
Communist Party of Great Britain
Volume 6
1962
Pg. 98:
The cynic who once said that “a government will do as much good as it must and as much harm as it can” should find ample confirmation in a detailed study of the Ministry of Health’s Hospital Plan.
   
Google Books
I, Claud ... :
The Autobiography of Claud Cockburn
By Claud Cockburn
Harmondsworth: Penguin
1967
Pg. 109:
“One should perhaps avoid being hypercritical of acts of high policy. Take the charitable view, bearing in mind that every government will do as much harm as it can and as much good as it must.”
 
Google Books
February 1988, Texas Monthly, pg. 144, col. 2:
Claud (Claud Cockburn—ed.) passed on to me the advice he had followed through all his years in journalism: Believe nothing until it has been officially denied, every government will do as much harm as it can and as much good as it must, always maintain a constant state of suspicious alertness.