there caterpillers of some sort so just go to your local garden centre and bye a decent insectiside . you could be more spaciffick and take the picture down the garden centre excuse my spelling lol and they could advise you egsactly what you need .

I have no idea what these bugs are - hoping someone else can ID them... sorry Scottish;-)

definatly a fury white caterpiller type thing .

Thanks Leigh and Bamboo - they are not a caterpiller - they are like the casing/cover of something but empty inside. The little beige bit on what I would call the head just picks of and the white stuff just wipes off. Kind of like the texture of dried toothpaste.
If they hadn't been on the underside - I would have suspected bird poo at first!!

strange

So presumably, something that has now hatched and gone... Is the rhododendron otherwise healthy?

It's looking ok now Bamboo - but was very poorly, didn't flower well at all and had a massive investation of aphids earlier on in the year. It's putting on lots of new growth. I had been putting it's troubles down the the lack of rain!! Obviously not a problem now!!!!
What ever it is - there is no sign of it on the new leaves and I only noticed this because one of the lower branches got broken off!
I treated the aphids with provado and gave it sequestrene as a 'pick me up' in spring time.

Well, you're doing all the right things...

Thanks hopefully what ever they are they are long gone and the plant recovers well.

Be interesting to keep a watch next spring, under the leaves, to see if they've appeared again, might be able to catch them at an earlier stage.

I'll do that. Cheers