For FMC past papers, go here.
https://www.primarymathschallenge.org.uk/fmc-downloads
(First Maths Challenge - an annual competition which is run by the Mathematical Association for students in lower Key Stage 2 primary school - years 3 and 4 (normally 7-9 years old)
For PMC past papers, go here.
https://www.primarymathschallenge.org.uk/downloads
(Primary Maths Challenge - an annual competition which is run by the Mathematical Association for students in upper primary school - years 5 and 6 (normally 9-11 years old)
For JMC past papers go here.
https://www.ukmt.org.uk/competitions/solo/junior-mathematical-challenge/archive
(Junior Maths Challenge - an annual competition which is run by the UKMT for students in lower secondary school - years 7 and 8 (11-13 years old)