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A very distinctive insect - the longitudinal stripes on the thorax confirm your ID. I bet it was on the edge of your pond...
yes thats right
Agree that the stripy thorax and general appearance confirm Helophilus, but it can be tricky sorting out the five species in this genus. Having said that, I agree that this one does look most likely to be H. pendulus, which is also the most widespread of the species.
Entomologist and biological recorder
.. and the one that is commonly seen around garden ponds.
Lat/Lng: 51.4, -2.6
OS grid ref: ST5970