It's in the northern sky. I first saw it at 8pm, it was still the same an hour later. I can't see the northern sky clearly where I am now, but it's coming up to 1am and I can still see a red glow in the same place (it's more pinky red than the photo shows).
Any idea what it could be? I'm assuming it's not a natural phenomenon given it hasn't moved or changed. I'm reminded of that tomato factory incident, but I don't know of any tomato factories in the area.
Edit: solved. It was coming from Spurs stadium and is probably lights to speed up grass growth.
I've looked up which directions I saw it. From both places it was in the direction of Spurs Stadium, so maybe they had an event on?
This happens in Cardiff quite often, also in the direction of the stadium. It seems to be caused by grow lights on the pitch which encourages the grass to grow faster.
If it is Spurs this could also be the case: https://www.tottenhamhotspur.com/news/2018/october/world-first-design-for-pitch-grow-lights-at-new-stadium/