It is natural for some of the fruit to drop and not mature. The tree sets far more fruit than it can actually support and this is its way of dealing with the situation. All top fruit do this.

Thanks for the comment but it is almost all of the fruit that is falling, I'm sure this cherry is big enough to sustain more than a handle full of cherries.

A few causes, lack of water at fruit setting time, frost at fruit setting time, lack of bees.

Thanks for the ideas, I think the watering is okay but still something to watch out for

Funny things Cherry trees, it well could be that despite the fruit looking as if it has set, it hasn't. Our self fertile Stella did far better when we got another Cherry which flowers at the same time, Morello. So it could be that you need to put in another one.

thanks again, if the fruit falls again this year I think I will try putting in another tree