Is this an Access panel in pavement

Well cannot see your picture, but Thames Water have something as you describe every few streets and the can use a kind of water pressure meter that looks a bit like a bollard which plugs in and one supposes has a cellular connection so they can track blockages or leaks. They only use them for a while of course, take that from one who has collided with many in my time of being blind! Brian

Robert wrote on 06/07/2019 :

It could even have been a coal hole. Some Victorian houses had their coal cellars extend out under the pavement, so were filled via a lift away panel in the public pavement.

Did they drop the coal lump by lump?

That is a small cover.

It happens that ARW formulated :

They used to be 12" x 12" so not much bigger that the quoted 200mm square. They would use a metal funnel to guide it in.