Heathrow Express is offering a discount of £6 on an Express (ie Standard) Class one-way ticket throughout October. This brings the price down from £21 to ‘just’ £15.
There is also a £5 discount on a return Express Class ticket, taking the price down to ‘just’ £29.
There are two conditions with this promotion:
You must book at least 7 days in advance
Only 500 discounted tickets will be sold per day with the total resetting at midnight
You must book your ticket during October although you can travel at any time in the next three months
If you want to buy a ticket at this price you should therefore try to do it in the morning!
The Heathrow Express discount code you need is OFFER15. This only works at the main Heathrow Express website.
It does NOT work at the version of the website which gives Avios points although you will still be able to collect Heathrow Rewards points via the main website.
Once this offer has expired, the cheapest deal remaining will be the 12% MasterCard discount outlined here. This deal runs until 31st January.