Fog prevents all aircraft leaving London Airport, and a group of passengers take an airline bus to another airport. The bus used "was MYV617 the original Commer-Harrington integral coach, still with BOAC at the time. It had previously been more(?) famous as an exhibit at the 1952 Motor Show." (thanks Martin Ingle)
Despite the coach being central to the action and on screen for most of the film, it's foggy and night-time, so clear views are difficult!
There are interior views:
It's not until the last minutes of the film that we see MYV617 reasonably well:
A continuity howler reported by Grant Hurlock on usenet: at one point bus driver Frankie Howerd shins up a signpost to read road directions in the fog. The sign says WET PAINT and he slides down with his uniform jacket streaked and ruined. However, several minutes earlier, as he leans forward to peer into the night, Howerd is clearly already wearing the paint-stained jacket!