Terry Casey wrote:
A friend went to Goodmayes station on Friday morning and asked for a single
to Southall, for which he was charged £5.10. He set off via Liverpool Street
and Paddington but when he got to Southall he was told his ticket was
invalid and he would have to pay again - £3.10.

He explained that he had asked for a ticket to Southall and pointed out that
the ticket included zone 4 (both Goodmayes and Southall being in zone 4.)

Wouldn't this be a case for a zero fare excess since the train-tube fare
is the same whether the destination is Zone U1234 or Southall?
--
Michael Hoffman