I am aware that 'break of journey' is restricted.
However if your journey is from Northampton to London and you travel on a non-stop train, albeit on a Rugby to London ticket, you have not by any credible stretch of the English language 'broken' your journey.
The CoC are clear:
"16. Starting, breaking or ending a journey at intermediate stations"
"You may start, or break and resume, a journey [...] at any intermediate station"
So as a starting principle you may start your journey at any intermediate station.
The exception to this is then given:
"However, these rights may not apply to some types of tickets for which a break of journey is prohibited, in which case the Ticket Seller must make this clear when you buy your ticket."
The text does not read
""However, these rights do not apply to tickets for which a break of journey is prohibited. The Ticket Seller must make clear if break of journey is prohibited when you buy your ticket."
or even
""However, these rights may not apply to some types of tickets, for which a break of journey is prohibited, in which case the Ticket Seller must make this clear when you buy your ticket."
It is clearly applicable to some tickets for which a break of journey is prohibited, but necessarily not all of them.
I would also add that with particular regard to London Midland, I just searched for Rugby - London tickets on the 15th January (arbitrary) date, and it offers:
"Advance Single
Origin:Rugby, 12:53
Destination:London Euston, 13:49
Date:Tue 15 Jan 2013 Changes:0 Duration:0:56hrs
Valid only on your chosen service. Not refundable. Changeable prior to date of travel for a fee."
The i button indicates:
"Break of journey:
You may not start, break and resume, or end your journey at any intermediate station except to change to/from connecting trains as shown on the ticket(s) or other valid travel itinerary"
which is clear.
But also
"Super Off-Peak Single
Origin:Rugby, 12:53
Destination:London Euston, 13:49
Date:Tue 15 Jan 2013 Changes:0 Duration:0:56hrs
Valid on off peak services, on date printed on the ticket."
Here the i button says
"Break of journey:
A break of journey is allowed unless otherwise indicated by a restriction shown against the ticket's Restriction Code."
As far as I can tell London Midland do not comply with the Conditions
"However, these rights may not apply to some types of tickets for which a break of journey is prohibited, in which case the Ticket Seller must make this clear when you buy your ticket."
It quite obviously is not 'clear', by any reasonable definition of clear whatsoever.
How many TOCs actually comply with this requirement in respect of off-peak tickets with BoJ restrictions (quite aside from the issue of whether a BoJ restriction means you can't start/finish short).
As a final note, if you can find the restriction text for the ticket (not sure how, from the LM website), unlike the text for Advance tickets, it does not say that starting and finishing short is prohibited. Again given the implication from the CoC that some tickets on which BoJ is restricted permit starting/finishing short, the omission of the text "You may not start, break and resume, or end your journey at any intermediate station except to change to/from connecting trains as shown on the ticket(s) or other valid travel itinerary", appears deliberate and therefore indicative that the general right to start/finish short is not counteracted by a prohibition of breaking journey.