John B wrote:

If Megatrain's condition A had the second sentence "break of journey
is prohibited", then it would. Presumably it's oversight rather than
any deliberate desire to create a loophole.

It also says on their web site on the "Travel by Train" page:

"""
My reservation states the main terminus; can I board elsewhere?
Please note that the departure and arrival times displayed are for the
main terminus points you selected. You must board and alight at these
points, and it is a condition of travel on megatrain that you may not
board or alight at other points on the route. If travelling on services
operated by East Midlands Trains, you will be charged the full single
fare for the actual journey made. On services operated by South West
trains Penalty fares will apply if passengers alight or board at other
points along the route.

Why can't I get on or off the train at intermediate stations?
megatrain is a simple low-cost inter-city fare like the successful
megabus which has been run by Stagecoach for over two years. It is not
expected to be highly profitable and must attract a good number of new
customers to justify itself. In order to do that, it needs to be kept
simple for passengers booking and simple for our staff to implement and
monitor. Therefore, megatrain is only being offered on lightly loaded
trains and between certain origins and destinations only. Should the
extension of the initial megatrain routes prove popular with our
passengers, we may extend to offer to more places.
"""

I think it's pretty clear that they intend that you shouldn't be able to
break your journey, and they've publicized this in their notices. If you
think otherwise, see if you can convince the magistrates.
--
Michael Hoffman