Worked STEP papers
Here you can find full solutions to some of the more recent STEP 2 and 3 papers, along with some commentaries and tips. You can use these however you like, you could use them to help you assess a "Mock Paper", or to see how you could have attempted the questions you didn't like the look of.
Browse the folder of past STEP papers. This folder contains all the STEP papers from 1987 to 2018, along with some of the markschemes and solutions (some of the older papers do not have mark schemes available).