I should have read the FAQ first....
Looks like you have to select ‘Mobile Ticket (NFC)’ option on the check-out page when you’re buying the tickets.
I didn’t even notice that option. I must have just been on autopilot and selected print at home.
When I have received wallet enabled email tickets from other companies (such as Cineworld) there is an ‘Add To Apple Wallet’ button that when clicked does the business.
There is no button on the email or the PDF tickets.