about 600mm from the boundary at the back, 900mm to the LH side. My problem is that adding a retaining wall adds another 300mm to the dimensions and already SWMBO isn't too happy. I think I'll see if i can take it back further, but I cant go any further left because of a laurel bush that I want to retain. If I can level it more on the left and leave just the need for a rear wall and grade the RH side a bit that should be OK. Else I'm looking at £700 of sleepers to make a wall, but at least that won't need a concrete foundation, just some post-crete'd holes. A poured concrete wall is another option at only .7cu m of concrete (100mm wide at top, 300 at bottom, 4.1 m long, 800mm high) but needs some complex form work and wouldn't look so nice.