I was there two years ago. London was dirty, lots of graffiti, and even more Muslims everywhere. There was an air of menace about the place, an undertone of unease.
The Brits are watching their country transform into Riyadh right before their eyes with the laws clearly favoring Muslims over Brits.
Reminds me of the quote attributed to Voltaire (paraphrased) ... if you want to know who rules over you look at who you're not allowed to criticize.
I was there twice in the mid 1990s. Yes old in parts and lots of iconic sights but I didn’t get those negative vibes you did. It was a big city for sure but in some ways the neighbourhoods felt like villages. Very sad how it changed.