Due to uncertainty about the new A levels many UK schools are switching away from A levels towards the IB.
2015: 472670 Home and EU students accepted university places through UCAS. Of those, 5640, 1.2%, were IB students. Suppose it doubled (and I don't believe for a second that it will) it would reach the heady heights of 2.4%. A lot of those will be, unsurprisingly, students from international schools, so its impact on UK university admission by UK students is very low. The has been a drop both in the number of schools and the numbers taking the IB in the UK since the early part of this decade, and the whole debate feels like a lost age.
... international A levels...Pre-U...
And? UK A Levels are well regarded internationally and, for example, the UK A Level is one of the few qualifications from outside the US which you can take as AP into US Universities. The Pre-U has little traction outside its originators: 4232 were sat in 2014, so that's, what, 1000 students? 0.25% of the UK undergraduate cohort (even assuming they were all applying to UK universities)? 1377 international A Levels were taken in the UK in 2014, so if they were being used as the sole qualification (I suspect that isn't the case) that would be less than 500 students. 0.1% of the cohort? Exciting stuff. A reasonably sized university with 10 000 home/EU undergraduates might have a couple of hundred students with either he IB or the Pre-U.
The idea that admission tutors in British universities come over all hormonal in the face of these minority qualifications and immediately reach for the "Accept" stamp, and the related idea that students who have these qualifications sweep all before them on arrival in a way that they wouldn't have done with standard A Levels, is a charming belief of people who are paying a lot of money to have their children at schools which offer them. But it has little basis in evidence, in large part because the numbers are so low: the typical programme will have less than 5 people with the IB, so the numbers will be suppressed in most HESA reports even if they were broken out separately, which they aren't.
These are perfectly respectable qualifications from good quality validating bodies, taught by good schools and accepted perfectly happily by universities. So are A Levels. The claim that they make the students ineffably better is mostly magically thinking.