I don't know what the ugliest building in London is, but surely the most tasteless is Harrods.
Passing it on the way to work at about 7.30pm it was all lit up with strings of bulbs, which sounds like it ought to have been appealing but was actually quite tacky. They were sickly yellowy-white and there were so many of them, so close together, that it looked like one of those houses that you see one of in every town at Christmas, where they've bought every single type of light that the local garden centre stocks and have covered the front with them, and turned them all on at once so that suddenly the government has to think about expanding the nuclear power programme just to keep up with the drain on the National Grid.
Then, driving home at 2.30am, I saw that the left-hand third of the lights were now green and the right-hand third were now red. There was no obvious reason for this – perhaps they had just restocked the food hall with Mexican or Italian nibbles and this was their way of promoting them. Who knows?
Whatever the reason, it looked quite ridiculous in the early hours of a September morning.