Pruning back a golden privet

[Pef]

Hi I have a golden privet border that needs about a foot off the top and one side, when is the best time to do this?

I have seen conflicting opinions on the net such as the autumn, the end of the year, or the beginning of spring - any advice of which month or time of year I should do this would be greatly appreciated.

I'm in the North East of the UK if that makes any difference.

Thanks