Hawkweed, maybe??

Yes, Orange hawkweed,(Hieracium aurantiacum on Sundays)
Its a great magnet for blackfly!

Thanks.

And runs like mad in decent soil

They are lovely !! Would having them in the garden keep blackfly on them and off other plants, or just lead to infestation? X

Yes. Hieracium aurantiacum (Orange Hawkweed)

I have a couple of 'clumps' of them in the garden.

They seed all over and spread themselves about, but I do like them. I am letting them go for the time being as I plan on using a big patch out the front of the house ( a spare bit of forestry land) to plant up with as many wildflowers as I can lay hands on.

They will come in handy for next year when I start on it.

Magna, they are incredibly invasive like most wild flowers himself accidentally introduced them into our old garden and we could never get rid of them, try as we might.

Fractal your plan is a good one just wouldn't recommend them for an actual garden.

Is it the same thing as 'Fox and Cubs', or is that a less invasive relative?

No Fox and Cubs is Pilosella aurantiaca and was introduced into gardens and escaped from there into the wild. They are both in the family Asteraceae.

Ah, I'd always imagined it was native.

Comes from North America Jonathan.

Thanks for identifying this - our neighbour has a few clumps that appear each year and I love them but because of the colour I've not been tempted to put them in my garden and sounds like it would be best to continue admiring from afar!