Congratulations in weaving the EU to blame, but you are very wide of the mark. Dredging is mainly done on tidal rivers, and it is not those areas that are mainly flooding. It might have helped at Fishlake, but the area has other problems. It was Fenland and peatbog. Over the last 150 years we have drained the marshes and built on it, and we have dug up the Peat. Compounded with flood defence schemes further up stream which have prevented flooding in major towns, only to transport the problem water downstream quicker to Fishlake..
The area had a months worth of rain in a day, and the ground was already sodden from steady rain over the last couple of months.