How can I mend Hayter 41 Quantum blade not turning?

I have a Hayter 41 Quantum and there are two issues:-

The first is that the blade has stopped turning. The underside is free of debris and the area around the blade has been oiled.

Secondly the engine hunts when the mower is running.
Michaela, June 2021


link Click here to see other fixes for Hayter.