Philip Hannon (Van Johnson) supposedly lives at Portman Square which is indeed close to Baker Street. However, the characters in the film go nowhere near Portman Square or Baker Street. His apartment entrance is at Portland Place but the back terrace overlooks the Thames (see the views below.) These views were probably taken from the Savoy Hotel.
View northeast – Waterloo Bridge, London
Central view – Cleopatra Needle (in the foreground), Shot Tower (now demolished) and Royal Festival Hall, London
View southwest – Hungerford Bridge, London
Jean Lennox (Vera Miles) and Bob Matthews (Cecil Parker) watching Hannon as he tries to cross the street all by himself – Portland Place at Weymouth Street, London W1. The view is from the southwest corner of the intersection, and it’s again inconsistent with the location of Hannon’s apartment entrance which is farther up north Portland Place.
The pub where Hannon overhears a conversation about a planned kidnapping – Mason Arms, 18 Titchborne Street, London W2. The pub and the street itself were razed during the area redevelopment. It was located approximately where the Water Gardens complex stands now.
Hannon and Bob’s boat ride – Waterloo Bridge, London
Westminster Bridge, London.
The police station – Paddington Police Station, Harrow Road, London W2. The station was demolished during the construction of the Marylebone flyover. The original blue lamp was transferred to the new Paddington Green Police Station.
Lady Syrett’s (Isobel Elsom) house – 50 Wilton Terrace, London SW1.
‘Unity Domestic Bureau’ – Queen Victoria Street at New Bridge Street, London EC4. The building has since been demolished to give way to Blackfriars Station.
Hannon’s apartment entrance – 74 Portland Place, London W1.
Bob starts following Alice MacDonald (Patricia Laffan) – Portland Place looking toward Regent’s Park, London W1.
Bob follows MacDonald to a department store – Barkers of Kensington, 63-97 Kensington High Street, London W8. The store closed down in 2006, and the building now contains a branch of Whole Foods Market.
Jean buys a newspaper – Trafalgar Square, London WC2
Janet Murch (Natalie Norwick) is murdered in a phone booth – the embankment by the Tower of London.
Hannon follows the fake "Mr. Murch" – Still searching for this location
"Mr. Murch" lures Hannon into a condemned building – Still searching for this location
MacDonald wheels DaMestres’ daughter across Kensington Road at Queen’s Gate, London SW7
MacDonald wheels DaMestres’ daughter through Queen’s Gate, Kensington Gardens, London SW7
Albert Memorial, Kensington Gardens, London W2
DaMestres’ house – 25 Kensington Road, London SW7
The Man Who Knew Too Much