That's the path. I lifted the flags ages ago, and dug a channel down the middle. There were some foundations along the edges of the flags, bricks, (and in one place, timber; why timber? not as if this garden has ever been short of bricks!) and I've dug them out. It remains now to dig down another 9ins or so, and then refill the trench with 3-4 courses of bricks. And then put the slabs back.
The grey drainpipe left middleground, I'm thinking of using a French drain, running down under the path and into the pond.
Lots still to do before Spring.