Lynnemary, I posted a blog a couple of days ago regarding just this problem. The RHS have said this:

Aphids are also spreading to plants they never used to feed on in the UK. The RHS is calling on gardeners to support research into an aphid that has only recently affected buddleia, causing distinctive distortion to the leaves. It is asking the public to submit information on the RHS website to help map its spread.

I have sprayed mine with soapy water as I don't use chemicals at all. I hope this helps you.

Sadly we are all affected by it Lynnemary.Even an 'escapee' Buddleja was covered with these 'blighters'!!

Lynne, here's link to Shirley blog on this, includes link to RHS for reporting
https://www.growsonyou.com/shirley_tulip/blog/36278-aphid-damage-on-buddleja

Thanks so much everyone who responded. I certainly hadn’t realised it was aphids.