alternator malfunction?

1993 200 TDI Range Rover
Hello everyone. I've used the forum posts before to help solve problems with my vehicle but I need some advice on my recent puzzle.
The battery warning light is staying on, dimly, and even increasing in brightness on increased revs. The battery is showing 12.5 volts open and the alternator belt is new and tensioned OK. With the engine running the voltage across the battery increases to about 13.8 volts but increased revs only improves this slightly. It never gets to 14.2 as suggested on posts I have looked at.
Does it look like the alternator is shot?
MOT due next month and body rot is now a serious problem. I've had the Rangie for nearly 9 years but it could be about to go. Shame because engine and other mechanics are fine-I think. It's been a lovely runner and I'll miss it. Anyway let's sort out the alternator first.

if alternator is not putting out 14 .5 volts,i think.then i would say its fecked.

maybe its the regulator on the back of the alty, and you might want to try and clean the brush(s), another thing that can cause that fault is a high resistance battery, how old is the battery and does it start the engine ok or does it struggle.
try another battery and see what happens if you can.