You can see this magnificent building from the Eurostar track as the train crosses the Thames 15 minutes or so out of St Pancras.
(This morning, I was on not Eurostar but the fast train to Folkestone. We’re bringing a dog to Brussels and you can’t take them on Eurostar. Instead you can get on a taxi in Folkestone and sit on it through the tunnel to Calais. Time: 7 hours compared to 2 on Eurostar. Cost: nearly double. But worth it.)
I looked it up on Wikipedia and found it is Littlebrook D, an oil-fired power station that closed down in 2015 rather than meet rising EU air quality requirements.