Looking for details of Southdown UF5755 seen in the movie The Weaker Sex

Two Optare StarRiders appeared in the TV show Playing the Field, one is Goldstar Travel, Stapleford PIB5768, the other is Camm, Nottingham M744LUC - what were their original plates?
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Trying to identify registration XV6848, seen on a derelict bus in the movie Things to Come

What was CK Coaches of Cardiff 25? Probably an Atlantean, seen in an Armchair Thriller, but the registration isn't clear.