Fred Astaire and Jane Powell are dancers whose contract runs out in New York, so they're in London at the time of the Royal Wedding. Actually, despite the use of some stock footage, it becomes clear that the stars never left Hollywood.
London Transport AEC STLs:
These AEC LTs at Piccadilly Circus should count as an anachronism, since none survived into the 1950s in front line service:
Now we see the odd narrow snouted bus seen in
Mrs Miniver,
Merry Andrew and
Darby's Rangers
A scene in a car has back projected London traffic, including this AEC STL:
....and this AEC Regal, possibly green, although the colours are slightly dull:
A scene in a small park has the fake STL passing again:
...but then something really odd appears! Seven years before the first production rear engine double decker hits the road in Britain, we suddenly see this:
This has to be the unique Yellow Coach 706 double decker built in 1933 and featured in several movies, including
The Snake Pit,
The Day the Earth Stood Still and
On The Town. I knew it found its way to California, but this brief footage shows it received red livery and London Transport fleetnames while there.
A continuation of the scene has the fake STL passing in the background again:
A scene on the day of the wedding shows a different bus - it's not even clear whether this is an open top 'decker or a charabanc, but we see no more than this:
...and lastly the fake STL comes into shot: