I would not cut it back while it is inside, unless you need some for cooking. It is already under some stress and removing parts of it would not help it at all imo. Sounds as if it might have powdery mildew. If it's big enough to carry you could put it outside on mild days and hose it down with tepid water a couple of times. Rosemary can take occasional temps below freezing without harm but if it's been indoors it's probably best to not leave it out if it gets below about 40.

Thanks for the tip. Though...I thought I'd heard that you should never allow rosemary leaves to get wet?

airing it also helps I got mine indoors by a draft let it dry completely out before watering it I let mine go two days bone dry and then let the soil get wet outside and bring it in

yippee1999 - it rains in the Med and it certainly rains on my 20 year old rosemary in England. It's out there now enjoying our latest 24 hour dose in a temperature of 39f. I do not expect it to die overnight. Providing it has good air circulation and good drainage no amount of water will bother it.

I din't know this about the rosemary I been going nuts putting holes in bottom pot now I be putting it out bring it in at night let it get soaked and a good airing

Yeah....see that's what I figured...don't all plants in the wild get wet? But then I know I've heard that before...that you shouldn't let certain plant leaves get wet...so are you saying that there really aren't any plants this would apply to? It would seem to make sense to me...that any plant should be able to get wet...and not just the soil part but the leaves as well. Unless maybe what it is is that...maybe depending on the environment in which you live, the air, humidity, temps etc. may not be such that any moisture on the leaves can easily and quickly dry out, much as it would for a particular plant's natural environment, and so maybe it's for this reason that if the plant is in a DIFFERENT environment, then getting the leaves wet could be detrimental because it will take longer for the moisture to dissipate from the leaves, which in turn could make them start to rot or something?

"....so are you saying that there really aren't any plants this would apply to?" .... no I'm not. I don't have the knowledge to make such a statement. We grow plants in unnatural conditions, as you say, so it is quite possible that wet leaves will be a problem for some. But not for rosemary. At least not if it has good fresh air circulation.

margowicz - are you saying you have been trying to grow your herbs up until now in pots with no holes in the bottom? That is a recipe for disaster with any plant in a container. When you water excess water must be able to drain out of the pot and it should not be left standing in water. Your rosemary could be left outside permanently in NI - but it must have drainage. I'm still looking forward to some pictures of your project. Any chance? If we could see them we could give much more accurate help.