With thanks to headforpoints and flyertalk, this link has been identified as giving you 10% off Heathrow Express (Paddington-Heathrow) tickets booked online.
Heathrow is obviously a key Air Malta airport, and notably the only airport outside MLA where Business Class upgrades purchased with KMiles have executive lounge access (the top class Etihad lounge, at present).
Given that, on a cost-per-mile basis, the Heathrow Express actually works out more expensive than flying to the moon*, it’s always worth knocking the price down a bit.
*This may not be strictly true, but it’s certainly extortionate.
Edit: this deal has now closed.