"Richard J." wrote
John Salmon wrote
This morning, I joined a westbound Circle Line train at King's Cross St.
Pancras.

What told you that it was a Circle Line train? I thought they were all
shown as "Hammersmith via Paddington" now.

It was described on the indicator at KXSP as Circle, and on the front it
said Circle Line to Hammersmith.

As we arrived at Edgware Road (platform 4) a westbound train was just
leaving platform 3, so our driver announced that passengers for the
westbound Circle Line should cross the footbridge to platform 2. I knew
that he meant the other kind of westbound Circle Line train, i.e. one
that would reappear as my kind in about an hour, so I chose to ignore the
instruction. But what should he have said to have made it clearer?

What exactly did he say?

He said exactly what I wrote above.

The use of the term "westbound" to refer to the line between Edgware Road
and High Street Kensington is not very helpful at all. "Anti-clockwise"
or "via High Street Kensington" would be a better description.

Exactly so.