When is the best time to cut down brambles?

Hello!

Opposite a line of 4 homes is a pond with trees. The pond was built about 13 years ago at the same time when the houses were built. In 13 years since it's existence the ground has not been maintained and brambles have overtaken (12feet high) the space, so now you can't even see the pond.

I'm putting a working party together to clear the brambles as the council won't help (!) A neighbour has raised the concern that to cut the brambles down now would possibly affect live bird nests from sparrows or blue tits. I personally have not seen any nests, but it did raise the question if it's ok to cut them down now? And if not when is the best time?

Your thoughts and educated opinions are much appreciated. 

Maany thanks for your help,

Tony