Tom,
There are no interviews at stage 2, just the maths test and the aptitude tests. Both of these are done on the computer. For the maths test, I would make sure you can do long devision and long multiplication without too many problems, and have a look at square roots and cube roots. Also, make sure you are comfortable using conversion factors (i.e. knowing whether to multiply or devide by them), you don't need to learn any before hand, you will be given any that you need in the question.
As the answers to the maths test are multiple choice (about 4 answers for each question) sometimes you don't need to work out the full answer, you can usually elminate some of the choices straight away.
Finally, the timing of the maths test can be tight if you spend too long on a question. Try not to get too wrapped up in working out an answer, if it is taking longer than a minute, take an educated guess and move on to the next question - you can always come back to it at the end if there is time.
I hope this has answered your questions.
Good Luck on Tuesday!