[6] Ridley was a student teacher and had made his theatrical debut in Prunella at the Theatre Royal, Bristol when he volunteered for service with the British Army on the outbreak of the First World War in August 1914.

[12] He served with the British Expeditionary Force in France during the "Phoney War", employed as a "Conducting Officer" tasked with supervising journalists who were visiting the front line.

In May 1940,[13] Ridley returned to Britain on the overcrowded destroyer HMS Vimiera, which was the last British ship to escape from the harbour during the Battle of Boulogne.

In 1918 he joined the company of the Birmingham Repertory Theatre, staying for two years and playing 40 parts before moving on to Plymouth, where he took a break from the stage when his war injuries began to trouble him.

[5] After being stranded for an evening at Mangotsfield railway station, near Bristol, Ridley was inspired to write the play The Ghost Train (1925),[10] a tale of passengers stranded at a haunted railway station in Cornwall, with one of the characters being an incognito British Government agent trying to catch Bolshevik revolutionaries active in Great Britain.

Ridley's post-war play, Beggar My Neighbour, was first performed in 1951[20] and adapted for the Ealing Comedy film Meet Mr. Lucifer (1953).

However, he became a household name only after he was cast as Private Godfrey, the gentle platoon medic in the television comedy series Dad's Army (1968–1977).

[28] Ridley died in hospital in Northwood in 1984 at the age of 88 after falling at his residence in Denville Hall, a home for retired actors.

[29] His body was cremated at the Golders Green Crematorium and an urn holding his ashes was buried in his parents' grave at Bath Abbey Cemetery.