This is Himalayan Balsam, a non-native invasive species. It thrives in damp places.

I agree. It's very pretty but one of the worst thugs. If it's in your garden it will take over.

When the seeds ripen, they explode and spread everywhere.

Efforts are being made to exterminate it where it is growing in the wild as it chokes watercourses.

Check whether your local Wildlife Trust knows it is there.

Thank you all for your prompt comments
Have notified wild life trust and put location on there map
Frae Longforganlad