If you are talking about quality in terms of research/scientific output, then there isn't much gap between the top 5 and the top 10. Places like Edinburgh/Warwick/KIngs/Bristol are extremely close to UCL/LSE, and not that far off Oxbridge.
If you are talking about prestige then making a "'top 5" is silly, because Oxford and Cambridge are just so far ahead of the others in the eyes of the general public. Its like asking for the "top 3 most famous football teams in Scotland". Whats the point, when the top 2 are so far ahead of the rest?
Most people in America for example don't know UCL ("do you mean UCLA?"), nor do most non-academics in Europe/Asia. I doubt it has more brand recognition than U of Edinburgh for example. Imperial isn't much better known either, although LSE does have a decent international brand name. But again Oxbridge are so astronomically far ahead that a top 5 sounds silly.
If you just meant employment prospects within the UK then sure, those are probably the top 5, but again I think its misleading to say that UCL/LSE are closer to Oxbridge than they are to (e.g.) Edinburgh/Durham, unless you are talking specifically about investment banking.