KS5 

www.unl.edu/amc/a-activities/a7-problems/problemdir
Mixture of longer Olympiad Style problems [A2 Level ]

www.risps.co.uk
Imaginative ideas to explore A level Core Mathematics topics

The following series of problems were prepared by Steve Wall (Stowupland High) were used as part of the video conferencing link between a number of local schools.
Problems 1 & 2   
Problems 3