Does anyone know what this is called?

Centranthus ruber or red valerian - there's a white form too.

Yes its valerian, I have it too and it gets everywhere but the insects love it so I allow it to stay and just dig up seedlings that are in the wrong place

Oh, I love it, Juliette.......I bought one last year from a garden centre and I'm pleased to say it's doubled in size....a deeper red than yours......they're a very useful herb, having a calming effect on the nervous system and Valerian tea taken an hour before going to bed, encourages natural sleep.

Depends on whether you like "weeds" (wild flowers) to self-seed in your garden. In its own way it's no worse than, say, forget-me-not. Provided your garden is not too formal, you can allow a bit of it to stay and pull out the rest.

Lucky you, it will not grow here at all. Tried it more often than I care to think about and it dies.

It is Kentranthus ruber, a member of the Valeriana-family.

Centranthus ruber as others have said. I have it in an area by the greenhouse with very shallow soil, having got the idea from the fact that they grow out of stone walls in the west country. I deadhead it after flowering - it still self seeds directly underneath but not so much elsewhere in the garden. It is _not_ the medicinal valerian, which is Valeriana officinalis.