[Shrezzing]

The UK has an age-based advantage in this metric. Oxford & Cambridge are nearly 1,000 years old. Once you take that into account, the stat becomes "of the top 8 universities (ex. Oxbridge), 2 are in the UK and 4 are in the USA". Imperial is very high quality institution, definitely the peer of Berkley/Yale. UCL normally isn't thrown into the top 10 though - it'd usually appear in the top 25.

[oblio]

The oldest university in the world isn't from the UK, so that clearly can't be such a huge factor.

[SeanLuke]

Bologna cannot be faulted for not being able to capitalize on its age.

Northern Italy went through an awful lot of tumultuous history between 1450 and now that England didn't experience: it was cut up into lots of little fiefdoms, dominated by several external powers, and generally kept under constantly changing iron thumbs.