200 years for a dam is really old. I hope it was maintained properly.
Supposedly all UK dams have an engineer allocated to them, and regular checks are done.
The damage in this case appears to have been done by an excess of water entering the reservoir due to heavy storms in the surrounding area. From what I can tell from the videos, an excessive amount of water went down the spillway, and damaged the concrete panels covering it. Once the water got to the soil under the concrete, it obviously started to wash the earth away.
There's a lot of Victorian infrastructure still in everyday use in the UK, they tended to build things quite well
One such item I 'discovered' a couple of years ago is the 'Derwent Aquaduct', it feeds water from three dams in the very North of Derbyshire to the cities of Nottingham and Leicester - a considerable distance. And it's entirely gravity powered all the way, and runs through tunnels, up and over large hills, it's really pretty impressive - and the only signs of it been there are the occasional stone built buildings that provide access points to it, and ventilation shafts that drop down to some of the tunnels.
Here's one of the buildings, you see a lot about if you start looking for them - notice that at some time the windows have been filled in, for security.