Winter damage! Don’t panic.
It’s easy to see the results of the recent cold snap as only negative but a bit of patience and you will see results.
Our Buddleja suffered in the cold (see the picture of one of our species) with leaf scorch from the ice and cold. First impressions and you would reach for the secateurs, some would even say it’s dead, I would strongly advise to hold back a week or two even down here in Cornwall before any pruning takes place.
The Buddleja in question already has signs of the green shoots of recovery and cutting back now, before the risk of further cold weather, could make things worse.
If you can put up with a little bit of untidiness for a few more days/weeks the plants will thank you for it and come the spring (which will be later this season due to the cold) the display will be stunning and worth the wait.