It's hard to see the bark and a single leaf's detail, but I'll take a stab at Acer pseudoplatanus, in other words, sycamore, one which has been stooled. Note that Acers as a group are deciduous trees.

This looks like an acer to me, also. There are many species of acer from the sycamore to the red leaved Japanese Acers in the garden. I am not even going to make a stab at id of it.

Thank you very much for your comments Bamboo and Bulbaholic. I have another question, as it is 'stooled' should I cut it back - if so when is the best time?

While its dormant, but before end of January is probably best - Acers tend to bleed badly once the sap rises in spring.