I think some of the plant experts only search for those that include "Plant ID" in the title or posts.
I for one, don't have the slightest clue what that plant is. But if I had to guess, I would say it may be some type of Ceratophyllum, some type of other wort plant, slight possibility of it being a Cabomba sp? But the bugs make the leaves look huge and the plant growth looks different from typical aquarium conditions. Maybe it's a type of fern very rare to the hobby? Again, I have no idea, just guessing from the look of the leaves.
For others to reference, I found some info on the water scorpions which might help narrow down what plant this may be based on the location and water conditions.
Water scorpion photo - Nepa cinerea - A8753 | ARKive
Seems they are widespread in Britain. Found in still and/or shallow waters. Mainly found in brackish water if I am not mistaken. Only get 1-2 inches max.