I dunno gb, Chicago* and Geneva (the only foreign cities I've spent an appreciable amount of time in as an adult, sadly) are both plenty different from London. And not just in terms of size, in the latter case, though obviously that's a big difference in itself. I was talking more just about the (lack of) difference between towns in this country, following crackerjack's point about the homogenisation of highstreets in terms of shops, pubs/bars, cinemas etc.
But yeah, globalisation is obviously a huge issue w.r.t. cultural/aesthetic homogeneity, as well as the bare economics of it.
It kind of depends what you're doing really. I mean, I live in London and I've just been to Paris and Barcelona, and would say that a lot of the shopping for consumer goods is similar if not the same, and a lot of the same chain coffee places exist (but don't really dominate, except in London), but otherwise it doesn't seem that homogenised - except insofar as urban bits southern britain, france and catalonia aren't that culturally different in the grand scheme of things anyway.
You still experience something quite different in terms of architecture, food culture, nightlife, media, lifestyle etc.
Homogenization of shops - I'm not sure how much this has actually affected london, particularly compared to the rest of the UK. I mean, you don't
have to stay on Oxford Street all the time. It's clearly a bit rubbish across the rest of the country though, especially in places that are too small to support Next, Marks and Sparks, H&M, Tesco
and some local independents.
Homogenization of restaurants and food culture is really noticeable and really bad across the UK - partly down to the rise of chain restaurants (which I think is in turn largely down to the fact that low-mid price British restaurants have traditionally been absolutely abysmal, and so generic, bland, predictable competence was actually an improvement - see also the rise of chain coffee shops in the UK) and partly down to a complete lack of interest at the reasonably priced end of things in local, seasonal produce and regional specialities. Both of which are fundamentally down to UK mass food culture having been mostly grim for years. This is something that does improve once you cross the channel IME.