From ‘Wings of the weird and wonderful vol 2’ by Capt Eric Brown

‘The Double Mamba is basically two side by side propeller turbine engines,each driving one prop through independent gear trains.The port engine drives the front prop.Each engine is a separate unit having its own fuel and oil systems,so that each one may be operated independently of the other.A common AUXILIARY gearbox is driven by either or both engines.’

He goes on to say that the first engine was started using a cartridge and normally the second was ‘windmill’ started whilst running the first engine at full power,although both engines had cartridge starters(saved on carts i suppose and probably a more reliable method of getting a good start!)
He also says that the Gannet was pleasant and stable to fly and a delight to land.

A long developement period for powerful turboprop aircraft was not unusual,even just the prop control systems were complex and quite a few military turboprop types failed to go into service successfully.