Is First Class declassified when a SWR 450 unit replaces an inner suburban standard class only service

[Meglos]

This afternoon I caught my local service from Chessington North into Wimbledon, which was operated by a pair of class 450's. https://www.realtimetrains.co.uk/service/gb-nr:L55960/2021-05-29/detailed#allox_id=0

I'm used to Class 455 & 456's on the service, along with the occasional Class 707's. However I don't remember seeing a Class 450 on the branch before.

I guess that this was a last minute substitution, as the down service to Chessington left Waterloo appears to have operated from Platform 20, on the Windsor lines, stopped at Vauxhall on the Windsor side on Platform 3, and then crossed the main lines between Queenstown Road and Clapham Junction to get onto the down slow line. https://www.realtimetrains.co.uk/service/gb-nr:L55939/2021-05-29/detailed#allox_id=0

The question I have is, is First Class considered de-classified on this service as there are no first class tickets available between Chessington and Wimbledon/Waterloo?

 

[yorkie]

The question I have is, is First Class considered de-classified on this service as there are no first class tickets available between Chessington and Wimbledon/Waterloo?

It is declassified, but not for that reason; it's because the train conveys standard class only.

 

[Journeyman]

Yup, the general convention applied anywhere is that if a train service is advertised as standard class only, and a unit with first class seats shows up on it, you can sit where you like on any ticket.