Described as one of the outstanding journalists of his generation, Mr Cassidy died peacefully, surrounded by his family, at Frimley Park Hospital on Sunday (April 9). He was 81.
As a freelance agency chief and national newspaper reporter, he earned the respect and admiration of colleagues and competitors alike.
Constantly on the alert for exclusives, Mr Cassidy led by example - and was renowned for scooping the opposition in a career the spanned more than six decades.
Born in Miles Platting, Manchester, in 1935, the son of an optician, Mr Cassidy loved nothing better than telling a tale.
Following national service in the RAF, he began his career on the Irlam Guardian before moving to the Sheffield Star where he famously “fixed it” for his pal Michael Parkinson to land a date with Mary, his wife to be.
'Legendary broadsheet paper'
From Sheffield he moved to the Empire News – a legendary Manchester broadsheet paper that sold on a Saturday night and Sunday morning.
He also worked on the Sunday Pictorial, which became the Sunday Mirror, and in 1961, he opened the Cassidy and Leigh Agency news agency, which was based in Eashing and later Hindhead, with his lifelong friend Don Leigh.
Mr Cassidy married his Spanish-born wife Maria Isabel in Seville in 1963 and the couple set up home and raised their family in Fleet.
Lured back to Fleet Street in the 60s, he was appointed senior reporter at the Sunday People in its heyday.
He worked on a procession of major stories and crime investigations before going back to the agency full-time in the late 70s.
In 1982, he was one of the founder members of the National Association of Press Agencies (NAPA) and remained its president and most outspoken advocate to the end.
'Journalism was his life'
Charles Garside, assistant editor of the Daily Mail, said: ”Denis was one of the great characters of Fleet street whose enthusiasm never diminished.
“I first came across him in 1978 when I became news editor of the London Evening News and ‘Cassidy and Leigh’ were among the most respected and prolific suppliers of copy.
“Denis loved life and, like all successful freelancers, journalism was his life.”
Former NAPA chairman, Chris Johnson, latterly of the Mercury Press, said: “Denis was a man of the highest integrity and a consummate professional.
“He was one of those great journalists who could charm his way out of any tight corner, and win the confidence of people to get the story he was after.
“Witty, entertaining, self-effacing, courageous and loyal, I would have trusted him with my life."
Devoted family man
He continued: “I saw him in hospital a couple of weeks ago, and even though he was weak he was laughing and joking to bolster other people’s spirits.
“He was devoted to his family and it was a joy for him to have them around him. I’m proud and privileged to know that he counted me amongst his friends.
“We shall truly never see his like again.”
Mr Cassidy is survived by his sons Paul and Ian, and daughter Raquel.
His funeral will take place on Thursday (April 13) at Our Lady’s Church in Kings Road, Fleet.
Family flowers only, by request.