Hi. I think this maybe a weed?

Purple loosestrife I think. Native to UK and Europe. Good for pollinators.

Lythrum salicaria as said. There are cultivated forms of it with bigger and different coloured flowers (shades of pink basically).

Thank for the info. I've now looked it up, I found that one can buy the seeds but I have got it for free, maybe from the birds or Wild Bird Seed? I think it is pretty & a lovely colour :o)) I found they like boggy ground so I will make an erea for it with some pond liner I have :o)) xx