Michael wrote:
...which lets me depart from Victoria but allows me to return to
Clapham Junction.

Personally I would have thought that a normal return ticket from
Victoria should be enough as, I thought, breaks of journey are
allowed. But I tried this before, the Clapham Junction barriers
rejected me, and the person at the gate let me through but told me it
was not allowed and not to do it again.

They are definitely wrong for an 'anytime' day - break of journey, and
starting or stopping short, is allowed on outward or return legs. The
published T&C are available he

http://nationalrail.co.uk/times_fare...onditions.html

"You may start, break and resume, or end your journey at any intermediate
station along the route of travel."

However station barriers are not normally programmed to allow intermediate
exit/entry, so you will need to use the manual gate, and a printout of the
T&Cs might be useful if they are being unreasonable.

Offpeak day has slightly different T&C:

http://nationalrail.co.uk/times_fare...onditions.html

"Break of journey is allowed on Off-Peak tickets unless restricted for the
journey you are making. If you intend to break your journey, please call
08457 48 49 50 to check if it is available on your specific journey."

The above has been the subject of much previous debate, (in uk.railway) but
it has been found that only the 'Intercity' TOCs seem to enforce this
generally, however the return leg is usually ok for break of journey anyway.

Access to the fares manual (which shows the restrictions for any ticket) is
no longer available to the general public online, but there are other
posters here who have access who may help, or you could ask at a ticket
office or even ring the number above, NR Enquiries...

Paul S