I've just asked a Belgrano chum about this. Whereas the CAA sent out a letter stating that you had to wait 2 weeks after failing a paper before you could resit another paper on the same topic and that you would have to wait another 4 weeks if you failed it again, they have softened this now, so that resits are 'at the Examiner's discretion'. However, fail any paper 3 times and you will have to wait 3 months before taking any other exams. You will have to obtain a certificate signed by your CFI saying that you are ready to attempt a further exam, pay a fee to the CAA and take the exam either at Gatwick or at your nearest regional exam centre.
So study those books!!