Different countries at different times have had different levels of censorship. Most famously the American Motion Picture Production Code (commonly referred to as the Hays Office or Hays Code) heavily restricted depictions of sex, violence etc). This covered major studio releases between 1934 and 1968. Although voluntary, the studios subscribed to its edicts rather than risk government censorship.

Kisses, their nature and duration, were very much restricted by Hays Office censorship. Famously Hitchcock filmed a scene in Notorious where Cary Grant and Ingrid Bergman got around the letter of the Hays Code by kissing many times but each kiss was very brief.

In Britain The British Board of Film Classification and its successors had a not-dissimilar role to the Hays Office. In that case distributors went by the BBFCs ruling in order not to have their film potentially banned by local councils. There were odd cases where a local council might ban a controversial film anyway, and even rarer cases where a council might allow showings of a film the BBFC had denied a certificate, but for the most part councils accepted the BBFCs judgement.

Television in both countries tended to have tighter censorship than feature films, even more so in the US than the UK. By the time of The Saint, British TV had shown more realistic kisses than US TV, which was always more prudish. However, The Saint, like other British filmed series made by Lew Grade's ITC company, was made very much with foreign sales in mind and so tended to avoid scenes likely to cause problems in other countries.