Is this a black spot on the leaves. Pick them off if you can.

Use a systemic spray that treats fungal disease and use an insecticide like Provado too, alternatively.
That's how i cured mine.

Thanks you for the replies and also for replying via my sister. I will give the spray a try. The tree is very old and 30 ft or higher so will not be able to pick off all the leaves.

I'll let you know how I get on.

thanks again