Help with ID-ing swans please

Hello! I'm looking for experts in swans:)

I cycled passed a large group of Mute swans today, and noticed a couple who looked quite different. My pocket guide instructs me that they're either Bewick's (smaller swans with a little bit of yellow on the bill) or Whooper (about the same size as Mute with more yellow on the bill).

Now, I'm confused. These 2 looked considerably smaller than Mute swans around them, yet their bills were quite yellow.

The encounter took place in East Anglia, a few miles away from the coast, if that might help.