If this was found in the UK it could only be
C. hypochaeridis or
C. aureolus as these are the only two large metallic species in this genus that sit on flowers in the UK.
It looks like the former to me as this species very variable ranging in colour from bluish, green through to red. Check out this site:
Cryptocephalus hypochaeridis
Where was it found exactly? Records for all the
Cryptocephalus species are welcome because none of them are encountered commonly.