I think the south side is the "official" Thames path, but I did think through London the north side was just as doable. I've walked the entire south side but not tried the north yet.

I do recall several difficult bits in the area you describe. One part seemed to have some new "food market" development, which was completely closed when we tried to go through. It got weirder the further we got and we questioned whether we'd gone wrong somehow. Eventually the path just stopped forcing us to double back and make for the road which added a mile or two to the walk.

We haven't had any such problems along to the west, all the way to Maidenhead so far.