[mumofstig]

The more you chop, the longer they will take to green up again, but privet has amazing powers of recovery even when cut back to the old wood.

One privet hedge in the terrace was cut down to the ground last autumn and has just started shooting again! So you can be as ruthless as you want 

[Paulj]

Just a quick thank you to everyone who pitched in to advise me here. I trimmed the hedge and although a little bare it looks much better than it did before-some me the neighbours have even commented on how much better it looks too!

[8doubles]

The more you chop, the longer they will take to green up again, but privet has amazing powers of recovery even when cut back to the old wood.

There is an unusual clause in the deeds of the houses on my street which doesn't allow the hedges to be replaced with other types of borders, so the ones surrounding all the gardens were probably planted about 80 years ago when the houses were built.
They have put up with being neglected and/or hacked about ever since (including by me!) but they still come back for more! 

Ours have had much the same treatment for 60+ years.
The only help they have had in that time is a bit of  guano from the sparrows !