The only possibility I can think of in terms of disease is Rhododendron Leaf Spot, but that usually causes irregular spots, sometimes with yellow around, sometimes concentric rings of slightly different darkness of colour, often with raised little black dots in the middle - its usually a purply brown. If you think its this, and its only one or two leaves, just nip off the affected leaves - if it becomes more widespread, you may need to spray with an appropriate fungicide treatment spray.

There are no yellow patches, no raised areas to the red/brown parts of the leaves. I'd say possibly about 30% of the leaves are affected in total so I'm not sure if I'd like to cut them off just yet, but would be willing to if it was a definate problem. I hadn't noticed any blackdots, although it has gone dark now so I will look again tomorrow to inspect closer. The colouring could be described as a purple though. Thanks for you feedback Bamboo. Much appreciated!

Odd, no idea as you shouldn't have had a real drought... Anything happening around the rhodo? Planted in a pot or in the ground?

I have added new pictures. The plant is in the ground, i added some of my own compost earlier in the year (you can see an egg shell on the ground). We do have a hose pipe ban due to the "lack of rain recently" all though I had watered my garden before the ban and it has done nothing but rain since the ban so I can't see lack of water or heat being the problem. The rhodo is also shaded by a tree. Ummmm. Hope its going to be ok.

I don't know whether its just the picture not being true, but it looks as if your rhododendron is on the top of a drop of some kind - if it is, then it would dry out quite readily, so drought could be a factor, but somehow, it doesn't look like drought. Think I'd be inclined to do a fungicide treatment anyway, it won't harm it.

Its on a slight bank in the garden. Possibly thats the problem then? I will also try the fungicide too. Thanks for the advise.