The best thing about this film is the fascinating period atmosphere. When this film was made, 1965, Britain, and British filmmaking, was exactly on the cusp between the old, class ridden, Imperial culture of films like 'Zulu', and the gritty, modern, realist school that began with films like 'Get Carter'.
In '65 Britain had a Labour government after a long period of Conservative rule, and sweeping changes were about to happen which would utterly change the face of British life. 'Ipcress' bridges the gap between these two eras.
On the one hand we have the upper-middle class army officers lunching at their clubs and strolling along in bowler hats with tightly furled umbrellas, and at the other extreme we have the way-out psychedelia of the interrogation chamber scene, and the grimy world of offices, warehouses, and men jumping out of vans that defined the TV and films of the 70s such as 'The Sweeney'.
In the middle somewhere is Harry Palmer, who rather than being working class, is classless. He has no discernable accent, dresses plainly, likes cooking and classical music and lives in nondescript surroundings. It is only his military rank, that of sergeant, that enables us to make any kind of judgement on his social status.
I think this is part of the enduring appeal of the film. Although the Dalbys of this world are long gone, Palmer would not be out of place in 2003, in fact the Palmers of this world are now the norm in many positions of British authority.
Overall a fascinating period piece but one which has worn well.