Looks like both the inlet shut-off and the flush mechanism are goosed.
I have removed all the internal gubbins to let the inlet water flow straight down the pan rather than filling the cistern. I couldn't shut off the water as the shut of screw is facing the wall and I couldn't get to it.
Being able to get into the workshop would have helped!
I will buy the bits I need today and fix it tomorrow.
The fill and flush internals have been replaced and the shut-off screw on the inlet pipe is now accessible.
If anyone wants to know how to shut off the water to the cisterns ask me and I will show you.