It looks to me like spider mites, but that level of damage would also include an ubiquitous fine webbing, almost like a nylon stocking pulled over the plant.

I don't know what this is, but it's interesting that its concentrated around the perimeter of the leaves.

Tugbrethil there are lots of fine webs immediately behind the plant on the fence. They've weaved in and out of the fence panels, do you still think that could be the cause? Thank you for your reply.

Bathgate It really is isn't it, I'm going to investigate again shortly ?

please let us know your findings, cheers

Spider mites weave their webs on the plant that they are feeding on, not elswhere. The webs may not be conspicuous in the early stages of the infestation, but you can still tell if they are present: put a piece of white paper under the affected foliage, and give that twig a sharp shake. If mites are present, they will show up as tiny tan, rust, or yellow-green specks running around on the paper. I also remembered that I have seen this kind of damage on plants infested with lacebugs.

Tugbrethil, you're absolutely spot on. I had a really close look and sure thing there are lots of webs in the middle of the plant and little beasties running about randomly. Even found a dead fly lying upside down on one leaf. I have removed the webs but what would be your best advice to alleviate/treat the problem?

Thanks

My favorite treatment is to use a strong spray of plain water to wash off the plant every morning for about 3-4 days, then spraying with water about once a week to keep them from coming back. I suspect that the washing doesn't actually remove many mites, but it seems to make life easier for the many kinds of predatory mite that feed on them. To ramp up, lightly soapy water will kill a few more, and seaweed extract will make that even more effective.

Excellent thanks so much, I'll give that a go and hopefully be rid of them. Appreciate your help very much. :)

if you have a magnifying glass focus it in the back of the leaf you may well be able to see what is there even a macro picture can show up a lot.