Roland Perry wrote:

In message .com, at
04:21:56 on Tue, 6 Jun 2006, Sam Holloway
remarked:
I thought exiting at Cambridge would be "abandoning" the journey which
is allowed at any station en-route. IIRC a BOJ would be if you left,
came back, and continued the journey

A house in Cambridge. Knock at door, circa 10pm
"Excuse me, sir, but it seems that you have abandoned your journey.
Please come with us, so we can put you on a train to Ely."

Airlines have attempted to surcharge people who buy a cheaper ticket
than only use part of it (they regard it as fraud). And they are usually
quite fierce about cancelling the whole ticket if you fail to turn up at
the origin [eg failing to do London-Paris on a London-Paris-New York
ticket.]

The only workaround appears to be to actually fly to the real origin on a
separate ticket. It is still much cheaper to do so for some airlines,
though.

--
Stewart Brodie