Unknown fruit

I have been looking at some of the threads and wonder if my question is among them
We have 5 trees at the side of our bowling green with fruits about the size of a golf ball ,on them they taste ok with a stone in them could anyone id for me many thank Colin

 

Looks like Prunus cerasifera nigra. Common name purple leaved cherry plum.

http://www.google.co.uk/imgres?imgurl=http://www.istockphoto.com/file_thumbview_approve/9638699/2/istockphoto_9638699-fruit-of-myrobalan-red-cherry-plum-prunus-cerasifera-nigra.jpg&imgrefurl=http://www.istockphoto.com/stock-photo-9638699-fruit-of-myrobalan-red-cherry-plum-prunus-cerasifera-nigra.php&usg=__OYUlGTo3tO-U5b-QJ_W5lixyzQA=&h=253&w=380&sz=69&hl=en&start=0&tbnid=ws8ZcYy1ZFYyXM:&tbnh=81&tbnw=123&prev=/images%3Fq%3Dprunus%2Bcerasifera%2Bnigra%2Bfruit%26um%3D1%26hl%3Den%26sa%3DN%26rls%3Dp,com.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7SUNA_en-GB%26biw%3D1244%26bih%3D528%26tbs%3Disch:1&um=1&itbs=1&iact=hc&vpx=761&vpy=128&dur=3281&hovh=82&hovw=123&tx=71&ty=45&ei=mhJgTIWyG9vPjAeBkYXKAg&oei=mhJgTIWyG9vPjAeBkYXKAg&esq=1&page=1&ndsp=21&ved=1t:429,r:4,s:0

Much asked about on forums this year. The fruit is edible.

 

I have a young P cerasifera 'Pissardi' which bore very little fruit this year ... and the birds ate that! :( It is truly a lovely tree.