Any ideas

Thankfully I gave up on roses ( or they gave up on me
so no damage there.
I've bought a Bayer product recommended by the RHS so here's hoping.
Daft question: will these caterpillar infestation be obvious?
Now that I've read up on the damage they can do it's obvious on some plants.

The garden centre man probably thought it was a ladybird (orange body. Dozey !)
We've had a few sawflies too.

There must have been quite an infestation if caterpillars somewhere if there are so many flies. Hope they weren't on your roses - they are voracious.

Ask the Garden Centre man if he'd like a few dozen for his own garden seeing as how they're so good for it...

Greyduster
First prize goes to you, that's what the little ** is.
Just have to read up on what do I do.
Thank you.

It could be a rose saw fly. They are not good for the garden!

Have you got any fruit trees? They might be fruit flies.

I should have added that the body is quiet a bright orange.