Four of the best universities in the world are in the UK, new international rankings show.

The rankings reveal that Oxbridge and London continue to dominate, with Imperial College London leaping into joint second place with Cambridge, and Oxford tying with University College London in fifth.

Institutions, such as Imperial, that focus on science- and maths-based subjects and research are increasingly well respected as governments see these areas as vital for their nations' future success, it is suggested.

The latest QS World University Rankings include eight UK universities in the top 50 and 19 in the top 100, up one on last year.

And a record six UK institutions made the top 20. Besides the four in the top ten, King's College London was 16th and the University of Edinburgh came 17th.

The Massachusetts Institute of Technology, in the USA, was first overall.

Ben Sowter, QS head of research, said: "Tech-focused institutions are increasingly the focal point of a global race for innovation.

"With budgets from public sources increasingly coming under strain, institutions seem more focused than ever on potentially-lucrative research in science, technology and medicine."

The Scottish universities in the top 100 are Edinburgh (17),Glasgow (55) and St Andrews (88). Graduates from Oxford and Cambridge were rated the world's most employable.