Walking northward through Camden recently, as I passed the the station and crossed Inverness Street I stopped occasionally to check that these manhole covers in Chalk Farm Road are still filled with wood blocks – yep. Good.
I went for a wander, musing that the markets here aren't markets any more, just Bansky and Winehouse opportunities surrounding some food outlets. I continued up the street then just after The Roundhouse, I found another wood-filled manhole cover within the large triangle of pavement at the corner of Regent's Park Road:


Only two segments retain wood, but that's enough for me!
A few days later I was ambling through the residential streets between Long Lane and Tabard Street in Bermondsey, SE1, and I found another man hole cover in Hankey Place, the wood almost hidden by the greenery growing within it. How lovely!

This broken line design is new to me – the lines are usually solid as per the one at Chalk Farm, above. We can assume that this was a specific feature of covers made by this particular iron founder, whose name is shown around the rim of the cover plate: Frederick Bird & Co., a name I have seen adorning many coal hole cover plates including those made by other companies such as Bartle & Co of Notting Hill Gate who implemented Bird's patented self-fastening locking system, as shown here.
Lots more lumps of London wood blocks here.