… she was surprised to find what looks like a well its about 1m dia built in bricks (all houses are stone) and full with clean clear water about 1.5 metres deep on pumping out the bottom is a clay type silt..

What could it be for? Is it a well if so how does the water get there as bottom end of garden is below the level of water. There isn’t any pipe work visible..
Also a question all neighbours seem to ponder would these houses when built have internal plumbing both supply and drainage (1865) and also gas? For lighting heating?
…
Probably a well, but don’t bet the farm on it without further investigation. People have many reasons for digging holes! To add to the list, it might be a French Drain, keeping the basements dry by encouraging water into a soak-away.
Whether or not it’s worth digging a well depends on the geology underneath. Usually taps into a waterlogged porous rock. This diagram shows some of the possibilities:

Most traditional wells were dug in the “unconfined aquifer”, that is a porous rock such as limestone laying on top of an impervious layer, usually clay. Water-table wells in the “unconfined aquifer” fill with relatively new surface water that percolates down from the surface. The surface excess flows into the stream. Though most water-table wells aren’t particularly deep, they might be. Castles on hilltops often have very deep wells.
Well water will be clean provided the water took many years to filter into it. Unfortunately, nature and man are both likely to fracture the rock, which allows dirty water to drain into the well, or the well might be fed from a nearby underground stream: dirty!
A well’s brick lining isn’t simply structural, it also keeps recent surface water out. Covers needed to stop animals falling in and festering. Wells had to be cleaned regularly because stuff grows in them and rots. In the country there’s space to separate earth closets and wells, but not in a town. There, it became necessary to pipe clean water in, and to pipe sewage away. At first sewage was just dumped into the nearest river or pumped out to sea. Both cause havoc; it’s necessary to treat sewage before returning it to the environment. Plenty of opportunity for ignorant or penny pinching opportunists to poison the wells, and they do!
The picture also shows Artesian wells, where water in a lower level is pressurised. Might gush out, not needing a pump, or fill an ordinary well close to the top. Deep water is millions of years old and biologically clean, though it will be mineralised – furry kettles! Couple of problems with extracting it: the surface can subside cracking up all the buildings on top, and, deep water doesn’t last forever.
Underground water isn’t always friendly. Some rocks dissolve in it creating caverns not far beneath the surface. Eventually the roof collapses and creates a sinkhole. I have family in Ripon near this house:

Piped water, gas, electricity, and sewage disposal took well over a century to spread. In the sixties house adverts still highlighted “All Mod Cons” if the home had them, because so many older properties didn’t!
Dave