Information and past papers for the UKMT Junior Maths Challenge, Intermediate Maths Challenge, Senior Maths Challenge, Olympiad and other competitions can be found at https://www.ukmt.org.uk/ . There are past papers and solutions for recent papers there, and others are available to buy (so I don’t post any here!). I have compiled below grade boundaries for each challenge:
And if you want a real challenge, or to see some amazingly skilled maths challenge competitors (Junior level) check out this video. It’s like ‘Are you smarter than a 10 year old?’ but with the world’s smartest kids doing maths!