Just over half of all teens go to university in the UK now. If the average IQ is 100 across the UK, then I suspect the sample size of the 50% that go to university is large enough to converge with the average of all Brits. So, my guess is that the average IQ of a uni student is 100.
Just to note though, IQ of X value doesn't mean anything because each test is different. E.g. when I sat Mensa tests, I had to take 2. On one I was in the top 2% of all test takers, on the other I was in the top 20%. On another test I could have done worse. It's a very flimsy, narrow and unimportant method to determine how smart someone is.