Update.

Flying back this Tuesday to LHR at 4.15pm.

Just had a look and it appears there are 30 unsold seats and 5 blocked seats. Meaning there are 3 upgrades available at the moment, which could increase nearer to check-in.

Looks like when online check-in appears I have to do a mad rush to the airport to try and get the upgrade, or do I have to wait until I get to the airport on departure day?

Not sure how this works. 4 passengers are travelling but only 3 available so far. I think online upgrades are for all passengers. Would like miles to be deducted from every passenger.