because with the engine off, I can select all the gears, and the car starts and runs with the clutch in, I suspect it is something to do with the throw out. Is it common to have a failure with this model at the throw out?
Yup you won't know until removing the gearbox. Then you can properly identify tbe problem.
But whilst its removed you may as well replace the clutch and slave no matter if thats not the issue. Change tbe gearbox oil as you'll need to remove tne half drive shaft abd thats if the gearbox is okay. Generally the petrols dont suffer any gearbox issues. Its very much over engineered the box to the ts or jts power output.