The Real Doctor wrote:

True, but there is typically only one unbooked carriage, into which the
displaced passengers from several other trains are unlikely to fit.

Seated probably not. There is no requirement for them to be seated, and no
rule against the entire train being "full and standing", which is generally
the best way to clear a mess like that.

Neil
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Neil Williams in Milton Keynes, UK. Put first name before the at to reply.