A type of fungus perhaps ..... someone with better knowledge will know what type.

looks more like wooly aphid to me. carefully wipe at it , is there a critter inside, or squish it and do you get redy/pink juice [urggh] if yes it is a critter and not fungus. you can treat with insecticide.

It could also be hydrangea scale, but by now, you should be able to find tiny yellowish nymphs on the underside of the leaves - if you find those, that's what it is - spray with insecticidal soap solution, but make sure you do it when the plant is not in sunlight.

thank you all for your help, but sorry to say, it has not got either of those symptoms when i wipe some off it just rubs away to nothing ??the plant it self seams so healthy and still has more buds opening.

Its still hydrangea scale - just means the nymphs have hatched out, leaving the empty egg 'cotton wool' behind. Keep a check next year if you're reluctant to treat, they can overwinter on the bare stems.

ok bamboo ,thank you for your help,can i buy that at somewhere like B&Q?,as i would like to kill it off this year if poss,thank you for sticking with me.I will get it and keep you posted

I suspect you might not find insecticidal soap there, you may need a trip to a large garden centre.

oh ok Bamboo thats no problem ,speak soon