Leaves falling off of rose bushes can be caused by different things, some natural and some due to fungal attacks. An attack of black spot fungus can cause the leaves to fall off of the rose bush -- In the midst of a string of intensely hot days, some rose bushes will become very stressed -- Another reason for rose bushes dropping their leaves is the lack of water --

In pots or in the ground? How long have you had them?

Thankyou for your answers. The roses were here in the ground when we moved in 4 years ago. They are flowering ok but not half as many flowers as previous years and the leaves that are still hanging on are pretty much covered with black spot. I have two bushes that are both suffering.

Seems like black spot is the culprit - you need to make sure you collect up all fallen leaves, don't leave any on the ground, then next year, after you've pruned in March, start a spraying regime in April, using Roseclear Ultra about every fortnight. It will help to feed them too, something like Toprose, once in April and again in early June, or mulch with composted manure (or both!)

thanks for the advice Bamboo.