Trees / Bushes

[Pullman]

Is there a right or wrong time to drastically prune, a holly tree which is about 20 ft at least,I want to cut down by half and some other tree / bushes which I want to do the same ( don't know what they are). Any advice would be welcome.

[Buenchico]

The RHS website indicates that the best time to prune holly is in late winter early spring:
https://www.rhs.org.uk/advice/profile?pid=549

[penelope2]

Light pruning in the summer, "drastic" pruning in winter/ early spring when trees/bushes growth is dormant. Good luck.

[Chipchopper]

With the holly, I think mid to late summer would be the ideal time, I did this to mine last year and its looking good now.
Cut the main stems about a foot below what you want the eventual hight to be, then you can trim off the regrowth and allow it to thicken up better.