Past few days noticed that whilst idling, a slight ‘ticking’ noise which made me think aux drive belt. Car is 148000 miles so was due. Last night battery warning light came on and long story short, completely discharged and alternator obviously not charging battery. Cam belt on inspection has virtually lost the ribbing on the inside of the belt and is starting to come apart. I’m quite happy to get a new battery and replace the aux drive belt and belt tensioner, however I’m not sure if a loose belt has any damaging effects to the alternator or other parts driven by the belt, in which case I need a garage as this is going beyond my own personal capabilities. Has anyone have experience of any problems

petrol or diesel ?

If the timing belt (cam belt) is breaking up, then it'll need to be sorted ASAP, as a broken or slipped timing belt will damage the engine, resulting in a cylinder head rebuild.
Having recently done a head rebuild myself on mine, I know it's many hours work, and so would be very costly at a garage.

The ancillary drive belt needs changing at the same time, but is quick and easy to do.

At that milage it would be a good idea to change the water pump while you have it in bits, its driven by the cam belt.