His father was a bank manager in London's Chancery Lane; his mother was one of the Dudleys, a Staffordshire farming family[1] He succeeded in winning a scholarship to Watford Boys Grammar School, from where he proceeded to St Catharine's College, Cambridge University, in 1920.

In 1935, he was appointed the first full-time editor of the staff magazine – The Old Lady of Threadneedle Street[2] Under his editorship, it became "a lively, absorbing journal of 200 sleek pages...packed with banking lore, poetry, literary articles, short stories and urbane correspondence, eagerly awaited and read by bankers all over the world.

"[1] The December issues of the magazine became referred to as: "Uncle Leslie’s Bumper Christmas Annuals"[3] During this period, he also published the Honorary Secretary's Guide (1938).

He was given responsibility for the 450 London balloons, for the movement of the numerous extra squadrons of them that they were assembling and seconding overseas; and for the planning and siting of any new barrages that were established at home.

At this time, he divorced his first wife, Getrude Olive May, and married Joan Hutt, whom he had originally met when she exhibited at the Bank of England.

The aim of the mission was to train the Chinese Air Force to operate as an independent service, rather than a branch of the Army as previously.

On a British aerodrome, the Chinese Ambassador to London awarded Bonnet the rare Order of the Cloud and Banner with Special Rosette "for distinguished services to China"[1] With the rank of Group Captain, Bonnet took up duties as director of studies at the RAF Staff College at Gerrards Cross until demobilisation in October 1947.

In 1949, Bonnet and his wife and family, along with 1,500 ducks and two dogs, moved to Criccieth in North Wales, where they had bought a ramshackle manor house with about 25 acres.

In his adopted home of Wales, Bonnet had the opportunity to write; he published numerous short stories, principally for Argosy, as follows: He also published plays, such as The Nine Fathers (1970), which won the Maynard Cup at the Wales Final Festival of One Act Plays in 1969,[4] as well as books such as Chinese Fairy Tales (1958).

He is buried in Criccieth Cemetery and there is woodland named in his honour close to Ymwlch, as well as a memorial bench on Garth Pier, Bangor.