Like many I encountered his work via his awesome contributions to the Games Workshop canon of classic images. It's a bit disappointing that his body of work for GW doesn't get any airtime in the interview as he created some stunning images for the company and gained a lot of fans as a well-deserved result. I thought I'd put up those images I could find which graced GW products including some White Dwarf covers. If I have missed any out, please shout in the comments.
I am lucky enough to own a copy of his monograph Blood & Iron which I highly recommend if you can find a copy at a reasonable price. In it there is a wonderful stage-by-stage series of photos an a commentary on his cover for Realm of Chaos; The Lost and the Damned (the last image in this post, sadly cropped to show only the book's front cover).
You can see Les' official site here.
Edit #1 - I had forgotten the Heroquest expansion Wizards of Morcar cover, which is by Les:
Edit #2 - this is the Ghoul piece reader The One has kindly pointed out was used by GW - he was on the cover of WD19. Weridly he seems to be flipped in some reproductions but I think this is the 'corrrect' orientation.