Sounds like Pyracantha Leaf Miner - its the larvae of a moth that mines into the leaves, causing the surface to look silvery. You should see some leaves rolled up, with sort of webbing inside, here and there as well. Doesn't kill the plant, but heavy infestations may need spraying - not sure what to recommend, since both the products listed to treat it with have been withdrawn from the market. Possible that Provado might work.

Hi Bamboo,
Many thanks for that. Just an idea, as it's hard to get hold of products to deal with the problem, would hard pruning help? I know it's not normally recommended for Pyracantha but just wondered if cutting out the problem is the answer. Also how can I prevent infestations in the future?

You can't prevent further attacks, it's just one of the things that Pyracantha might suffer from in certain areas of the country. Yes, you can clip off affected parts, but if the infestation is heavy, all parts might be affected, which means you can't cut them all out. Check out Provado Ultimate bugkiller or others in their range, they probably have something that deals with leaf miner.

Brilliant! many thanks, so glad I found this site. Def going to be a regular from now on.

Oh, sorry, didn't realise you were a new member - welcome to GoY!