When Bullitt was first released in the U.K. in January 1969. (It was submitted to the BBFC British Board of Film Censors in Autumn 1968) it was initially given A certificate (the 1968 A rating stood for Adult No One Under 12 Admitted Without A Adult Parent/Guardian And May Not Be Suitable For Under 12s).
The 1970 version was the same but the age limit for a child to see an An rated film without an adult was reduced from 12 to 8.
There were only three rating certificates for films in the UK in 1968. They were U ( Universal For All Ages), A (Adult No One Under 12 Admitted Without An Adult Parent/Guardian And May Not Be Suitable For Under 12s ) and X ( Adults Only No One Under 16 Admitted With Or Without A Adult).
But in 1970. a new AA (No-One Under The Age Of 14 Admitted With Or Without an Adult) certificate was introduced as part of changes to the certification/classification system (which led to the minimum age of the X rating being raised from 16 to 18 and the minimum age for a child to see A-rated film unaccompanied by an adult was reduced from 12 to 8).
This was a result of the changes in July 1970 re-rated by the BBFC from A to AA, as Bullitt was an unsuitable film for the A under the 1970 rules.
Bullitt: Release in U.K.–Censorship, Ratings