I have friends at many of these schools and I will try to rank them in terms of general international prestige, especially in terms of undergraduate education.
(Note alphabetic order for same rank - !)
1. Penn (Wharton)
2. Oxford
3. Dartmouth, LSE (economics), Penn (other schools)
4. Berkeley, Brown, Cornell, Duke, LSE (other subjects), UCL
5. Durham, Vanderbilt
Now to arouse some controversy I will also rank the top schools of the US and UK together. Note! I am trying to not be biased here. It is a bit difficult to compare for example narrowly oriented schools like Caltech and Imperial with others. Also, I only rank these in terms of international prestige, not pure UK or US domestic prestige, nor for any specific subjects - engineering at Cornell for example is generally regarded as better than at Harvard.
1. Harvard, Penn (Wharton), Stanford
2. Cambridge, MIT, Oxford, Princeton, Yale
3. Caltech, Columbia, Dartmouth, LSE (economics), Penn (other schools)
4. Berkeley, Brown, Cornell, Duke, Imperial, LSE (other subjects), U Chicago, UCL
Note: Yes, I believe the US comfortably edges out the UK overall, but remember that the US has a population many times that of the UK so I suppose you could say the UK is more impressive 'per capita'.