Solved Popping seed pod plant

That's Himalayan Balsam and, as the Rivers Trust say:-

It is prized for its delicate pink flowers, Himalayan Balsam was first imported to the UK during the mid-19th century as an ornamental garden plant. By 1855, it was spotted growing in the wild. Since then, this innocent looking shrub has taken over river banks and lake shores across the country, quickly reaching invasive status.

Why it’s a problem: Himalayan Balsam grows in dense thickets and projects its seeds up to four meters away, meaning it can quickly dominate any ecosystems it’s introduced to. These thickets can impede water flow, as well as leaving river banks vulnerable to erosion when dieback occurs over winter. Finally, Himalayan Balsam pollen proves particularly enticing for visiting insects, which researchers believe may decrease the pollination of native plants.

Removal: Removing Himalayan Balsam is a time-sensitive matter; it must be dealt with before the seeds set. Due to their shallow roots, these plants can be pulled out and disposed of appropriately, which means composting them or even burning them if seeds are present. Repeating this process on a regular basis should be enough to achieve control, as long as seeds are not allowed to set.

In the Lake District the National Trust found it took years to get rid of this very invasive plant. This is what they had to cope with.