Oh, London is notorious for having... questionable internet speeds in certain areas. It's good if you live in a new build flat/work in a recently constructed office building or you own your own home in a place OpenReach have gotten to yet, but if you live in an apartment building/work in an office building more than 5 or so years old?
Yeah, there's a decent chance you'll be stuck with crappy internet as a result. I still remember quite a few of my employers getting frustrated that fibre internet wasn't available for the building they were renting office space in, despite them running a tech company that really needed a good internet connection.