It may be a dogwood, Cornus species. It would be helpful to see a sharp photo of a leaf.

Yes, Dogwood is very likely given the location. Bird sown Cornus sericea plants are common because cultivars are widely used for winter colour or variegated foliage. I get them on my allotment all the time from the neighbouring park.

This post was edited by floral_uk on Mon, Sep 29, 14 at 7:17

Maybe a suckering buckthorn? I'd like to see a closeup of the leaf too.

Buckthorn is not a very likely candidate to pop up in a UK garden.

Of course, floral_uk. I wish everyone would put their location in their names :-) I sometimes forget to check "My Page".

Here's a close up, thank you for the help so far!

Yes, that's a Dogwood.