Ken said "You reach a point where the underground will become literally intolerable and you could face the prospect of loss of life." Although he's offered hundreds of thousands of pounds as a reward to find workable air conditioning for the underground, it sounds like the heat will eventually defeat the system. He believes we will have to resign ourselves to closures "if the temperature goes up faster than we fear it's going to".
Personally I think the only way there would be loss of life would be if people were stuck in the tunnels during a heatwave. But as getting stuck in tunnels for more than a couple of hours is becoming increasingly more frequent, perhaps Ken has a point.
We discuss intolerable heat on the Tube, year after year after year, but is the solution really to roll over and admit defeat like this? Surely there must be some systems somewhere in the world that we can learn from?