Couldn’t find this in the Wiki, but here’s an update which I encountered yesterday regarding the complimentary upgrade to 1st on HEX (Heathrow Express)

I’ve only used this a handful of times, and only had 2 ticket inspections on the train anyhow. But was on the HEX yesterday and GGL card acknowledged, and with my guest also, but I also used a 241 Railcard, and was advised that both discount ‘offers’, ie using a Railcard and upgrade to 1st cannot be combined, it’s either one or the other. So to use the 1st upgrade you can’t use a Railcard or in fact any other promotion. This then got me thinking when travelling alone I always use the BA On Business 10% off code, so this would I’m guessing fall into the same trap!

So the information seems to be if you want a Free upgrade to 1st you need to buy one of the specific 3 full price standard tickets. This would also rule out the 30-90 day advanced tickets!

Obviously for a 15 minute journey you’d have to weigh up if the 3xtra cost of giving up your other discounts is worth it!

The Railcard issue is bizarre however, as a full priced Standard return is £74 in order to get the free upgrade, but a full 1st return with Railcard discount for 2 is £72.60, so it’s cheaper if you want to travel in first, to just buy the discounted 1st ticket anyhow!