Hello Valle:
One is full price, and the other one is cheaper, called “supersaver” ticket. Both say that fare is reduced with Half-Fare travelcard. Am i allowed to buy and use the supersaver ticket, even though i don’t have half-fare travelcard?
No. You can only purchase Supersaver tickets at half fare if you will have the half fare card on the day of travel (not required at the time of purchase, though).
You can purchase Supersaver tickets at full fare.
Keep in mind that Supersaver tickets are not recommended when you will arrive by air; in case of a flight delay, the Supersaver ticket is no longer valid.
Kind regards,
Roland