I looks like a Lysimachia ciliata cultivar, perhaps 'Firecracker'? Phil J

No - can't be...that would have yellow flowers at this time of year, and the ones on the allotment appear to have red ones!

I have seen this before - it's a type of edible leaf, but I'm blowed if I can remember its name! Some people use it as an ornamental plant, too.

Orache? Atriplex hortensis Red Mountain Spinach

I think that has rounder leaves, Ob. My candidate is one of the edible forms of Amaranth--Amaranthus tricolor, or A. hypochondriacus.

That's the one, Ob! Orache. I saw it at an open garden earlier this year.

Tug may well be right in his ID, though - I'm just pleased to have my memory jogged. :-))

Red Orache , it does spread and seed I pull them up every year ....... the leaves make a colourful addition to salads ......

Thank you all so much for your answers! :-)

I did a search for "Red orache" & I think you are right. It seems it is you are right, Owdboggy, it does seem to be Atriplex hortensis: Red orache, aka French Spinach. Apparently you can use it like Spinach. It also seems very popular with the Romanians! It seems that in Romania they use it a lot in a soup.

The things you learn on the WWW!