The heater pack should be behind the glove box. Remove the glove box and there should be a plastic box with an electrical connection on it. Get a stubby philips screwdriver, remove the two screws and lift off the resistor pack. One of the coils will have snapped off. Scap yards are best for them, only about a fiver, you might need to check a few cars for a good one though. I think the rover 25 has the same pack, just check the serial numbers. While the glove box is out, there is a metal bar running top to bottom with a plastic stip behind it. Remove the plastic strip and the pollen filter is behind it, this will likely need changing if the coil has burnt out. A blocked filter causes the coils to dry out and break.
Does anyone know if a '96 Rover 600 (the one with the Honda 2.1 engine) has the resister in the same place?
The blower works on all 4 speeds if you give it a slap under the dash. I think it's more likely to be the motor itself on this one. I've had the glove box out and the motor looks buried and nothing like the nice easy 3 screws out job the Rover 800 I once did.