You're going to get a longer answer because I don't know where you are in the UK - if you've had rain since the flowers appeared, this could cause balling, which a lot of roses do if they get rain on their flowers, and that's what it looks like in the latter picture. I don't know though, because you haven't said where you are in the UK - if you're in the south, that won't be the explanation.

Thanks for the response.
I live in Gloucestershire and have many other roses which are flowering beautifully.
Petor

Not all roses respond this way to rain on their blooms - if this is Iceberg, that one's very prone to this problem.

Could it possibly be rose thrips, Bamboo? I have had the same problem on a white climbing rose. Someone suggested thrips, because of the drought and told me that they prefer pale coloured roses...come from Scotland, so never experienced thrips before!
...said person didn't offer a cure though...

Capsid bug causes buds to go brown and not open - thrips can usually be seen on the half open flower as little black marks all round the top of the bloom. This definitely looks like balling from the rain to me, but Petor hasn't said whether they had significant rain whilst it was in flower.

I can't see any bugs, so rain balling it is. I'm surprised they sell a plant that is as sensitive to a bit of rain as that. It will have to go. Thanks.

Choose carefully when you get a replacement, Petor - bear in mind that most white roses seem to have this trouble, although there are others which do too.