Littleham's husband is probably right. Its not that these Universities have problems recruiting good UK students but that good UK students have problems getting places, certainly on the most popular courses.
These courses have Europe wide and International appeal. In some cases it is easier for an International student to get a place. Universities certainly seem to like the International students who have done sixth form at academic schools in the UK. EU students legally have to be given equal treatment with UK students. Some of this is fine. The demand from strong students from across the world is almost certainly helping keep our leading Universities towards the top of world rankings. The arms race, in terms of grades required, is keeping ambitious UK sixth formers pinned to their desks, as they realise they need to compete with the world's best in order to gain places at top institutions. (Look at the explosive growth in AS and A2 Easter revision courses - the i newspaper had an article yesterday.)
The losers might include employers looking for a steady stream off graduates who then find these graduates are looking to go home whether to Italy or Korea, or have simply seen the UK as a stepping stone to a Masters in the US.
(UK Undergraduate degrees are simpler to apply to, courses are often more specialist and only take three years, and international fees can be significantly cheaper than those for world ranked US institutions.)
And perhaps those UK students or their schools who are not aware of the extent to which the bar has been raised for the top ranked maths based courses. At a recent talk at the LSE the Director spoke of his concern about the diminishing proportion of non-London, non-private school, non-Southern UK students they were able to attract. He suggested they were considering adding a second, less quantitative economics degree that more UK students would be qualified to apply for. Trouble is that the quantitative degrees are in such high demand because they open the doors to equally quantitative post-grad or Masters degrees.
To me something needs to be done about the education system so all secondary school can deliver students to the right standards in maths, thus reducing the need for "contextualisation" amongst the UK cohort, and allowing all UK applicants equal chance to compete with overseas/EU students whose secondary systems have traditionally taught maths well.