Large insect, looks like a hornet. But it’s a hoverfly, imitating a hornet to protect itself, so it’s no threat.
Hornet hoverflies were first recorded in Britain in the phoney war summer of 1940. They are extending their range, but even presumably up to date websites say that they are just found in south-east England, with very occasional sightings in the south-west.
This one was feeding earlier today on the flowers of a thyme in Wolverhampton. It’s a female – the males have eyes which meet in the middle.