Gregson was born of Irish descent, and grew up in Wavertree, Liverpool, Lancashire, where he was educated at Greenbank Road Primary School and later at St. Francis Xavier’s College. He left school at 16, working first for a telephone company, then for Liverpool Corporation, as the city council was then known, before the Second World War started. During this time, he became interested in amateur dramatics, joining first his local Catholic church theatre group at St. Anthony’s, Mossley Hill, and later the Liverpool Playgoers’ Club. When war broke out, Gregson was called up and joined the Royal Navy as a sailor on minesweepers. At one point, his minesweeper was torpedoed and he was rescued from the sea with a knee injury. After being demobbed in 1945, he joined the Playhouse in Liverpool for a year, before going on to Perth Theatre in Perth, Scotland. Here he met his future wife, actress Ida Reddish from Nottingham, who at the time was using the stage name Thea Kronberg and had recently arrived from the Birmingham Repertory Theatre. In 1947 they moved to London and married there. They eventually had three daughters and three sons. He was credited as ‘John Gregson’ in 40 films between 1948 and 1971 and on television from 1960 until his death. He was often cast as a police inspector or as a navy or army officer, or for his comedy roles in Ealing and other British films. One of his first appearances was in the film Saraband for Dead Lovers, a tearjerking romance starring Joan Greenwood and Stewart Granger.

Gregson’s best known role was in the comedy Genevieve (1953), also starring Kenneth More, Dinah Sheridan and Kay Kendall. More was described as his “rival” in British cinema at the time, although Gregson tended to appear in fewer comedy films and more dramas. He also appeared in the Ealing comedies Whisky Galore!, The Lavender Hill Mob, and The Titfield Thunderbolt. His best known drama films include The Battle of the River Plate, Angels One Five and Above Us the Waves. He was featured in The Treasure of Monte Cristo and had a role in Treasure Island. Gregson also worked on TV. In Ivor Brown’s BBC TV play William’s Other Anne he played William Shakespeare revisiting his first girlfriend Anne Whateley. TV work became increasingly important to him from the mid-’60s. He starred as Commander George Gideon in the 26 episodes of the series Gideon’s Way (known as Gideon C.I.D. in America). He also appeared in The Saint with Roger Moore, and a popular comedy adventure series with Shirley MacLaine, Shirley’s World. He took over from Kenneth More in long-running TV adverts for coffee on British television. He appeared in It’s the Geography That Counts, the last play at the St James’s Theatre before its closure in 1957. John Gregson died before retirement and suddenly from a heart attack near Porlock Weir, Somerset, aged 55, whilst on holiday, walking on the path to St. Beuno’s Church, Culbone. He left a widow, Thea Gregory, and six children. His final television role was in the Southern Television serial Dangerous Knowledge, which was broadcast posthumously in 1976. His body was interred at Sunbury Cemetery, Sunbury-on-Thames, Surrey near his family home at Creek House, Chertsey Road, Shepperton.