These issues should be dealt wih by the resident and the council were appropriate.
With matters of appearance to gardens it is always worth having a little chat with the neighbour before taking any action, as this could resolve the situation before involving any outside bodies.
If greenery from a private dwelling is overgrown and encroaching onto a footpath to the extent of reducing the width of the pathway or forcing pedestrians off the pathway into the road, the Council should be notified.
The Council will then instruct a designated Streetscene Officer to view the situation. If after inspection it is felt action needs to be taken, a letter will be issued and if no action is taken to remedy the situation, the Council could have the greenery cut and then bill the occupant.
If the overgrown area is a Council responsibility, the Parks and Woodland Dept. should be contacted.