Freelander 2 (LR2) Alternator problem

This morning the red battery symbol on the dash illuminated a few seconds after the engine started. I had to complete my journey, about 20 miles, before I could check things out.
Here's what I found.

Engine stopped, battery rested for 1/2 hour: 12.5V
Engine running: 13.6V at the battery.

Put known good battery in parallel using jump leads (battery doesn't fit the tray unfortunately) and disconnected the -ve to car battery. Voltage 13.6V with engine running. Upping the revs makes no difference

I know, from checking caravan battery hook-up a few weeks ago, the alternator did chuck out 14.4V at idle.

Looks like my alternator is duff, unless anyone has another idea.

Is replacing the alternator a DIY job? Looks an absolute sod to get at.

It’s making charge, it probably needs just a new diode/ regulator pack fitted on the back, if you can remove, £200.00 tops at your local auto electric guy
Just had one done, so that’s where I get the pricing

Or you could give it to @gstuart to solder the new one on !

Update.
Engine running, headlights, main beam, fog lights and heated seats all on.
Voltage at the alternator 13.4V, same at the battery, so not a bad connection in the charging circuit.
Fault Code P065B Generator Control Circuit Range/Performance.

£200 for a diode / regulator pack when I can get a new LR001200 20008 ALTERNATOR FL2 2.2L DIESEL 180AMP for £233.

The alternator I had repaired was a high output from a john Deere , replacement was about £600, hence a repair was in order !

freelance said:

The alternator I had repaired was a high output from a john Deere , replacement was about £600, hence a repair was in order !

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You must have some electric hungry accessories! The one I'm being quoted for is a 180A alternator.