If the train needed to be evacuated it would be helpful to be able to
announce that to all the passengers... Not just to disabled
passengers

The guard is quite capable of going down the train.

operating. What's wrong with getting off at East Croydon and getting
on the next service which stops at Gatiwck Airport? They are pretty
frequent, aren't they?

Ever tried to get a full train load of passengers + luggage into an
already
full train in the rush hour (or anytime for that matter)?

B2003