ians3, redhand, slob -- you're all correct.... Was ye old fanbelt !
bought a brand new wider one, it doesn't sit a far down the pully... used a small rachet strap to get alt in position and tensioned up, horsed all the bolts...
Started 13.6V, all lights on and heater, 13.6V
Well done Chaps! free pint or two if we ever meet up!