Suffolk, United Kingdom

Can anyone help ID this please.
It's doing it's best to cover the hawthorn hedge. It's a woody shrublike thing with dull green leaves & impossible to pull out. When you try to dig it out the root leads you to the next one that's popped up & so on. So it grows like couch with a rhyzome type root. No thorns or spikes tho.

I'm still trying to ID this hedging type plant & have added another pic in the hope that someone will recognise it. The closest I've found is that of the Alder but I haven't seen any catkins or cones so am not convinced but did find this which again fits with its behaviour:
Note on Alder roots: Alder has invasive roots that can break old water pipes and damage the foundations of old buildings or walls. 30 metres away from vulnerable structures is a safe distance to plant Alder.

The hedge is a very old country hedge on my boundary.

• 18 Jun, 2015