I purchased this frame last October from a Bike Forums member. The frame (even with the paint imperfections) is beautiful, just too small for me. The photos that I've included are of the way it was built up by the previous owner. I rode the bike twice since I've owned the frame.
From the resarch I have done, Clark's of Harrow was a cycle shop in Harrow, London in the 1950s-60s. It is not clear to me if Clark's of Harrow produced their own frames or if they branded frames from other London builders. One London builder, Wally Green, built frames for Ivor Clark of Harrow during this time period, so it is possible that this is a Wally Green made frame from the late 1950s. You can read more about Wally Green here:
The frameset has a 56cm seat tube (c-t) and a 56 cm top tube. Chain stays are 17". I think the photos show the condition reasonably well--some chips all around but particularly on the left-side chain stay, but the finish overall is in quite good shape and the lug lining is well preserved. Reynolds 531 db tubing, Simplex rear dropouts.
Price is $150 plus actual shipping cost. Sale includes frame, fork, seatpost, and Campy headset (which has some external pitting, but bearing surfaces are good).
More pictures are available in the gallery here:
Clarks of Harrow