I unearthed this 'percussion hand tool' whilst gardening in Bush Hill Park, Enfield.
It appears to have been worked from a naturally axe shaped nodule. It is extremely tactile with multiple comfortable grips, both left and right handed. Although it weighs about 775g it is finely balanced.
I have identified some similarities to other finds which may be of note.
Wessex Arch. Swanscombe handaxe http://www.flickr.com/photos/wessexarchaeology/2293741006/ - the cortex has been worked to resemble an inverted 'J'.
A handaxe in the Thomas Layton Collection (tagged Hanwell: 0.65 on powerpoint presentation) http://www.thames-explorer.org.uk/Thomas%20Layton.html is not dissimilar in profile, size and shape.
The nodule's natural contours may have been shaped but extensive hand wear/use is evident. A distinct 3cm - 4cm 'V' has formed on front centre neck where different grips have crossed. The location of the impact points dictates the optimum grip and each of these have left their individual wear patterns. I've identified over 10 grips, including 5 left handed. See http://www.flickr.com/photos/27757493@N07/2587824589/ for more photos.