"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 the 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."
Above I have quoted the relevent clause from, the conditions of carriage. As Yorkie says, this conbination is not valid, as the Haywards Heath-Croydon season is not a zonal ticket, Gatwick Express services don't call at East Croydon, and both tickets are season tickets. It was posted in another topic on the board recently that LT travelcards don't count as PTE tickets.