If it is mildew, spray with 1 part milk to 9 parts water. And no, I'm not joking...

Lol, won't that make it smell? I think its mildew, it comes off with a wipe of my finger and its sort of powdery.

If it looks white or grey as well, it probably is, though I wouldn't have thought it was warm enough for that right now. Not sure skimmed milk is as effective as either full fat or semi skimmed though... and it won't make it smell, the danger is it'll get rained off before it even works. You can always use a fungicide instead if you want to.

Is this 'mildew' on the top or the bottom of the leaf. 'May Day' leaves naturally have a thick, fuzzy, cinnamon brown indumentum on their undersides and it is part of the attraction of this variety.

No its more on the branches rather than the leaves Bulbaholic. I've taken a photo and will see if I can add it to the question. I see what you mean by the underside of the leaves, it almost looks like suede effect!

That's not mildew, looks like algae or lichen. You can clean that off with a wet cloth.

Thanks Bamboo will do that... what's the reason its there? I'm new to gardening and might ask some silly questions but I'm keen to learn!

Don't know. Looking at those leaves, bottom left, it doesn't look too nice to me. I have not seen this before but would not say that it looks like lichen I know. Maybe give it a spray with copper sulphate.

Well observed, Bulbaholic - your comment has made me have a closer look. In the second picture, I note that the stem on the right has a much greener part right at the top - is the plant healthy other than the deposit on these stems? Do the leaves look good, no parts died back or limp or discoloured?
Now I've looked at the first pic again, there is evidence of this deposit on the base of the leaf stems - I'd be inclined to spray with a good fungicide (not sure copper sulphate is still available) - but I'm not sure what the problem might be. Do you have lots of wild Rhododendron ponticum in your area? Are you near woods or forests?

We have woods in our village probably about half a mile maybe less away from me. I would say the rest of the plant looks healthy to me. I've just taken another couple of photos of the whole plant for you to have a look at. Thanks ever so much for your help, it really is appreciated.

Well the whole plant looks fine, doesn't it. I'd spray with a fungicide just in case I think, and keep an eye on it to see if anything else develops.

Thanks Bamboo, will do that.

Do you think that it might be beneficial to prune this small piece out, Bamboo?

I'm not sure I'd worry about it too much, Bulbaholic - if the fungicide doesn't work, and the plant gets ill, it might have to be disposed of - I'm wondering about phytophthera ramorum or kernoviae... but only time will tell.

Hope not.

That's the trouble when new diseases hit - there's a tendency to jump to the conclusion its one of those if you don't recognise the problem. And it may well not be.

I do hope I don't have to dispose of it, I only bought it about a month or 6 weeks ago. I will get a fungicide tomorrow and see what happens.

Then you should contact the nursery where you bought it from and advise them of your/our concern. They may have a real problem themselves and should not be offering infected stock for sale.

Bulbaholic's right - I'd return it to where you bought it.

I'll give them a call tomorrow.

Has it been waterlogged in a small pot?