Today all you can see of the famous River Fleet is a collection of streams running pure and free on Hampstead Heath. They are the same streams that once fed the second most famous river in Britain, after the Thames, which it joined just 5 miles distant in the bustling heart of London.

Its final 2 mile stretch is the reason much of old London is sited where it is. But people abused it, and polluted it, and in time the entire river, defiled beyond measure, was driven underground and turned into a sewer.

The writer walked the line of the river's short length, and found many fascinating associations – landscape, people, literature and fascinating history.

Now there are plans to bring the Fleet back to the surface. It's becoming easier to imagine that some time in the 21st-century the Fleet will flow again, clear and fresh, above ground.