Oh dear. Last November our c.30 year old holly was covered in red berries. Then came the first snow and freeze up and when the snow melted the holly was covered in black berries. I had never seen that happen before. From then on this large holly just became more and more poorly. Leaves dried up and fell off more and more frequently until it was obvious, even to me, that it was dead. I cut it down a few weeks ago.
I don't know if that is what has happened to yours but it is my story.

Would help if we knew where you are in the UK Trulyblu

yes, more questions from me too - where are you in the UK, I echo, and also, how long have you had the tree, and is it in a pot or in the ground?

Hi, sorry it has taken me so long to say thanks for your answers. I live in Somerset. The holly tree we have is quite old. The berries on it now are fine but it still loses lots of leaves all the time. it is in the ground where there is plenty of sunshine. I have also noticed recently that there is strange bug on it that I cannot find info about. They seem to be in white flat looking pods.

Hi, just a bit more. The bugs that come out of the pods are black scaly looking and quite visable!!

Be good to see a photo of these bugs, but if they're on the woody parts, trunk and branches, it could be scale insect.

They are only on the underside of the
leaves

We still need a photo

ok, see what I can do!