What are you on about relex?
Split Advance tickets
do not require you to get off the train. If you think they do, then by what 'letter of the law' are you referring?
National Rail Conditions of Carriage 19(b) allows you to use multiple tickets for one journey, does not exclude Advance Purchase and does not require you to alight at your split point, you're train merely has to call at the split point.
19. Using a combination of tickets
You may use two or more tickets for one journey as long as together they cover the entire
journey and one of the following applies:
(a) they are both Zonal Tickets (unless special conditions prohibit their use);
(b) the train you are in calls at a station where you change from one
ticket to another; or
(c) one of the tickets is a Season Ticket (which for this purpose does not include
Season Tickets or travel passes issued on behalf of a passenger transport
executive or local authority) or a leisure travel pass, and the other ticket(s) is/are not.
The guidance issued to staff regarding use of a combination of Advance Purchase tickets also explains that if you are travelling on two Advance Purchase tickets that requires a change of trains then if the train from A-B is delayed, you are permitted to take the next service from B-C with the same operator of your original booking. The only condition the passenger must meet is to have allowed the minimum connection time (as defined in National Rail Timetable) at the station where they are changing trains.
From guidance issued to staff ('The Manual'):
Advance fares - Frequently Asked Questions
Q04 - Can a customer buy two Advance tickets which join together to make one journey, e.g. ticket for A-B plus ticket for B-C, to travel the throughout journey A-C?
A: Yes, provided the train calls at B
Note 1: Where a passenger buys multiple Advance tickets in this way, if they then have to change their booking, it will also cost them multiple amounts of ^10 fee.
Note 2: Where separate train companies are used for A-B and B-C with a change of train and ticket at B, it is still classed as a through rail journey in the event of delays (see also Q22 below) provided connections were booked in accordance with the advertised minimum times for stations. For example, a passenger travelling Cambridge to Leeds holding a combination of Cambridge ^ Peterborough ^XC▸ only^ and Peterborough ^ Leeds ^EC only^ is allowed to take the next East Coast service in the event of a delay on the CrossCountry journey causing the connection to be missed.
Q22 - Can a passenger travel on any trains other than the one on which they are reserved, without changing the booking?
A: The following principles apply.
1). Start of the Journey. It is the passenger^s responsibility to turn up at the start of the journey in time for the first train. If they miss it due to problems parking, taxi not turning up etc, they must buy a new ticket;
2). Once the journey has begun. If the passenger is delayed and the rail industry or its partners (as shown below) is at fault, which should be checked with your Control Office, change to another train of the same company is allowed to get them to their destination with the least delay. This is irrespective of combinations of rail tickets held.
It's really most concerning that someone at the top of the industry is going on record and coming out with poppycock.
It's also concerning that a member of rail staff appears to be misinformed.