Opal Citizen Science – https://www.imperial.ac.uk/opal/
RSPB Schools Birdwatch – https://www.rspb.org.uk/whats-happening/get-ready-for-big-schools-birdwatch
Big Butterfly Count – https://bigbutterflycount.butterfly-conservation.org/
Garden bio blitz – https://www.nhm.ac.uk/take-part/monitor-and-encourage-nature/bioblitzes.html
A range, some seasonal, some location specific – https://www.countryside-jobs.com/volunteers/citizen-science
A range of Scottish projects – https://www.nature.scot/citizenscience