I would say, just about, and probably not for much longer – London.
Britain still retains a heritage of being at the heart of scientific advancement for centuries, from the enlightenment to the industrial revolution.
It’s probably declined since then, but London still has a good number of some of the great universities, it has some of the greatest museums (and associated research) in the world, has some of the greatest scientists in the world and it is well connect to both America and Europe.
If you asked in 5-10 years I think the answer would be somewhere in Asia. The east is increasingly catching up and will probably overtake everyone else in the world at a lot of stuff fairly soon.
If you asked in 15-20 years I think the statement would probably have no meaning – science has taken to the internet very well and become distributed. Everyone collaborates with everyone else now, no matter if they’re in a different country or a different continent. So I don’t think I’d be able to answer the question in a few years.