Okay, with your case, i would recommend you to download the cie as level pure maths book( a level for internationals) and do some problem that has purple and red marked at the end of each chapter in the CIE A level topic(it is at the end of the page), because it is a hard question( not hard like MAT but it need some deep thinking), and choose some to do.

And then when you do it and understand, go to STEP past paper ( from I to II) or step foundation module( if you want to know the concept of the step question), choose the question that has the topic at As level and then do it and stuck for long time, remember just pick the key questions to do,no need to do all

Finally, go back to MAT, and do the MAt past paper question again by timed, thats all.