Personally, as someone who revalidated last year, I thought the Oxford PPL CD's were terribly badly produced. In my day job, I deal with a lot of online and digital learning resources, and these CD's are shockingly bad from a production perspective.
Unfortunately, the UK student pilot population is so small compared to the U.S. that there is a relatively small market meaning that there is no real driver for someone to invest the money in producing good quality digital training resources.
Some of the U.S. AOPA online courses are very good in my opinion, but these are geared to licenced pilots.
However,
AirQuiz - Online Practice Examinations for Pilots! is excellent value for money if you are a student pilot in the UK - as a complementary resource to studying with the books, not as a replacement.