What if I skip part of the itinerary by means of walking / alternative transport, in order to catch an earlier train than the itinerary provides?
For example, I have an Aylesbury - Apsley return ticket with itinerary 19:12 Apsley - 19:41 Euston and 20:57 Marylebone - 21:53 Aylesbury on the return portion, however as I don't need to stop off at London while returning, I leave the train at Watford Junction at 19:20, walk to Watford to take the Metropolitan Line, take the tube departing 19:52, transfer to the Amersham train at Moor Park at 20:01, then the 20:18 train at Rickmansworth to the ultimate destination Aylesbury scheduled to arrive at 20:52 (61 minutes before the fastest National Rail itinerary).
Unfortunately the Chiltern Railways train is delayed by 30 minutes. I then put in a Delay Repay claim for the Rickmansworth - Aylesbury leg, claiming that I broke my journey and resumed at Rickmansworth upon returning. Will a man on the Clapham bus think that I really broke my Apsley - Aylesbury journey?