The BBFC received Ken Loach's Kes for classification in May 1969. The original examiner reports written for the classification of Kes in 1969 are unfortunately no longer available, but letters sent by Stephen Murphy (BBFC Secretary 1971-1975) in reply to complaints made about use of bad language in the film do reveal the thinking behind the classification of Kes. Two of these letters are published here.

In 1969 only three certificates were available from the BBFC - U (universally suitable), A (more suitable for adults) and X (suitable for over 16s only).  In 1970 the BBFC revised the category system, introducing a AA certificate (over 14s only) and raising the age restriction for X certificate films from 16 to 18. The A certificate was an indication that a film may contain material that might be unsuitable for children, leaving the U certificate as a clear marker of films that should be entirely suitable for children.

In a 1972 letter, Murphy informs the complainant that "our current 'U'... does, we hope, guarantee no offence to anyone, and we have the new 'A' to fall back on". He goes on to make clear that a higher category than U would not have been considered for Kes in 1969, and a U certificate was the most appropriate category for the film at the time - "with the categorisation then available, to have given KES anything but a 'U' certificate would have been positively immmoral".

In another letter from 1972 Stephen Murphy explains "the positive values of the picture were more than compensation for any irritation caused by some authentic dialogue, much of which, for example the word 'bugger, is not regarded as offensive in the area where the film was shot (indeed it is often a term of affection)."

When Kes was submitted for video classification in 1987 the ratings system had changed to include categories that the BBFC uses today, i.e. U, PG, 15 and 18. For the video rating the examiners noted the frequent use of mild language, and felt a PG certificate was the most appropriate category. Kes remains a PG today.