If they are all Buddleia davidii varieties, including the dwarf ones, yes - but you can do it during March, doesn't have to be at the end.

The later the better, even leaving it until April. One of the National Collection holders prunes some of his as late as May to get the best flowers in August to attract the emergent butterflies.
Your choice, as the pruning will determine the flowering time. However, too early (i.e.: now) and a frost or cold wind could damage the newly stimulated growth.

Thanks for that info buddlejagarden. I never realised it was ok to leave them later. That would really help me up here is scotland, as they often get frosted during April.