Information and resources for the STEP exams (primarily used for entrance to Cambridge and other universities) can be found at the official Cambridge website and past papers can be easily accessed at the official admissions testing website. In particular there are foundation modules to prepare for these exams. The syllabus for these papers goes beyond A-level content so you will need to do extra work to prepare, beyond just practising past papers.
The Maths Helper website also has a well organised archive of past papers going back a long way. The STEP Database website allows you to search for individual STEP questions all the way back to 1987 by topic.
Note – STEP is changing for the 2019 examinations to reflect the new A-level syllabus and the number of questions in each paper will decrease from the current format. The official website says more detailed information will be provided in summer 2018.
Below are links to video solutions I have made to selected questions from some STEP papers.
STEP 1 Pure Maths Questions
|2016 STEP 1 Question 1||2010 STEP 1 Question 1|
|2016 STEP 1 Question 2|
|2018 STEP 1 Question 1|
STEP 1 Probability Questions
|2016 STEP 1 Question 12|
|2016 STEP 1 Question 13|
STEP 2 Probability Questions
|2017 STEP 2 Question 12|