Harry Palmer, a British Army sergeant with a record of insubordination and a criminal past, now working for a Ministry of Defence organisation, is summoned by his superior, Colonel Ross, and transferred to a section headed by Major Dalby.

Ross suspects that Radcliffe's disappearance is connected to the fact that sixteen other top British scientists have inexplicably left their jobs at the peak of their careers.

Afterwards, Dalby tells his agents that the main suspects are Eric Grantby and his chief of staff, codenamed "Housemartin", and orders the team to find out where they are at present.

Suspecting that Radcliffe is being held in a certain disused factory, Palmer orders a search, but nothing is found except a piece of audiotape labelled "IPCRESS" that produces meaningless noise when played.

Dalby then points out that the paper on which Grantby had written a false phone number is the programme for an upcoming military band concert.

Carswell has discovered a booklet titled "Induction of Psychoneurosis by Conditioned Reflex under Stress" – IPCRESS – which he believes explains what has happened to Radcliffe and the other scientists.

Sangster enjoyed the book and was eager to adapt the novel, suggesting Michael Caine to play the main role and Sidney J. Furie as director.

But from the opening scenes of the film, Sangster's screenplay identifies Caine's character clearly as someone who cares little for authority, who indulges in quick repartee and has an interest in good food.

[12] The final screenplay included contributions by Sangster, Bill Canaway, James Doran, Lionel Davidson, Johanna Harwood, Lukas Heller, Ken Hughes, and Deighton himself.

Saltzman wanted The Ipcress File to be an ironic and downbeat alternative to the portrayal of espionage in Ian Fleming's novels about Bond and the film series which followed from them.

In contrast to Bond's public school background and playboy lifestyle, Palmer is a working class Londoner who lives in a Notting Hill bedsit and has to put up with red tape and interdepartmental rivalries.

The format was introduced by Technicolor Italia in 1963 and allowed for a greater depth of field as it was shot with lenses of shorter focal length than those used in the anamorphic widescreen processes.

While enjoying the first part of the film, and generally praising Michael Caine, the critic found the second half bewildering to the extent that the characters "cease to be pleasantly mystifying and become just irritatingly obscure.

"[2] A review in Variety was largely positive, describing the film as "anti-Bond" for its unglamorous depiction of espionage, and praising Caine's understated performance but criticising the sometimes "arty-crafty" camera work.

Decades later Michael Caine returned to the character in two made-for-television films produced by Harry Alan Towers: Bullet to Beijing (1995) and Midnight in Saint Petersburg (1996).

A television adaptation of the same name, directed by James Watkins and starring Joe Cole as Palmer, premiered on ITV on March 6, 2022.