First check the plant from top to bottom, including all small branches - you're looking for damage, infestation or disease, soft rotting areas, anything at all that's unusual. If you can't find anything obvious, is the tree in a shady spot compared to the one near the house? Is it drier there, or very wet? Is there grass growing around the base of the tree trunk, or nothing at all? There may be some difference in the growing conditions between the two trees - work out what the differences are, because something about the environment is not suiting the tree currently.

I thought they liked a little lime, I found this though.

http://www.ehow.com/facts_5790358_should-soil-ph-cherry-trees_.html

So far as I'm aware, they're not fussed about ph apart from Prunus laurocerasus varieties, which don't like chalky soils, Pimpernel.

I thought that as well Bamboo, generally happy anywhere. When I said " a little Lime" I meant a trace of, nothing more. The link I provided suggests a very narrow tolerance of a PH between 6.2 - 6.8 not what I was expecting at all.

Trouble with EHow is that the information they provide is only as good as the person who compiled it. The RHS suggests flowering cherries in various places in their publications (online as well) as being suitable for any soil, so I'm sticking with them!

The flowering cherries (prunus) prefer an alkali soil and as your camellia seems to be flourishing, points to your soil being acidic. As already suggested it might be a watering problem, cherries tend to be surface rooting, so they can easily suffer from lack of water. They also suffer from bacterial canker, so look for an oozing of discoloured sap. A good mulch wouldn't do any harm.

thankyou to all who answered my question sonia