[citation needed] Thomas entered the film business as a clapper boy at Shepperton Studios in 1932 during his summer vacation while at college.

[1] During the Second World War, Thomas served with the 9th Lancers rising to the rank of Major and being awarded the Military Cross.

[2] Thomas left the army in 1945 and re-entered the film industry, although he could only gain work as an assistant editor.

Thomas later said making trailers was "enormously useful" because he "learned a lot of the technique of how the varying directors whose pictures I had worked on operated.

We knew that we were not always doing very creative work, but that there was a chance to gain experience and that this wasn't going to last... You were quite likely to finish shooting on Friday, plan to go into the cutting rooms on Monday to look over your stuff and get your cut ready, then go for a drink, and you'd be given another script and be told, 'The sets are standing and you start on Monday – this is the cast!'

[6]While assembling trailers, Thomas met Sydney Box's sister Betty, and the two of them struck up a rapport.

However, when Thomas left Sydney Box to go under contract with the Rank Organisation to make The Clouded Yellow (1950), he brought Betty with him as a producer.

The film made a star of Dirk Bogarde and led to a number of sequels, all of which would be directed by Thomas.

He followed them with the less popular Checkpoint (1956), a noir crime thriller concerning car racing starring Anthony Steel and featuring location filming in Europe.

The success of Doctor in the House saw Thomas offered to direct the Cold War comedy, The Iron Petticoat with Bob Hope and Katharine Hepburn.

This success encouraged Rank to finance Thomas and Box for a series of expensive adventure films starring Dirk Bogarde shot on location, aimed at the international market: Campbell's Kingdom (1957), A Tale of Two Cities (1958) and The Wind Cannot Read (also 1958).

Also on a large scale was The 39 Steps (1959), starring Kenneth More in a remake of the Alfred Hitchcock classic, which was a box-office success.

Thomas returned to comedy with the smaller budgeted Upstairs and Downstairs (also 1959), starring Michael Craig.

Thomas did some uncredited work on Carry On Cruising (1962), before making a university drama with Box, The Wild and the Willing (1962), an "angry young man"-style melodrama which was the first film for Ian McShane, John Hurt and Samantha Eggar.

In return, Rank agreed to finance Thomas and Bogarde in two more expensive films: the James Bond spoof Hot Enough for June (1964) and a serious look at the Cyprus Emergency, The High Bright Sun (1964).

He then made two Bulldog Drummond films, both starring Richard Johnson, Deadlier Than the Male (1967) and Some Girls Do (1969).

[citation needed] Thomas later described himself as: A sort of journeyman picture maker and I was generally happy to make anything I felt to be halfway respectable.