By the way is there much difference between ox and cam interviews (assume you applying for the same subject say)
Yes and no.
Oxford send you round the different colleges for strings of interviews over the course of 3-4 days depending on whether your 1st choice college has filled up its places already or not. Cambridge give you 1/2/3 interviews at your first choice college over one or two days. Some Classiscists get interviewed at New Hall also, which is kind of a 'pool' college due to low application numbers. Then at Cam you either get rejected, offered, or pooled. The pooling takes place in the first week of Jan where other colleges who have had lower numbers of applications get to pick and choose candidates to fill up their places, from the pool.
Interviews are quite similar, assessing your knowledge of the subject applied for, aptitude, and ability to think on your feet- think random questions and logic questions, plus impossible ones.