Alternator replacement FL1 TD4

Hi folks,
The battery light on my 2001 FL1 TD4 was coming on intermittently whilst driving and now it's on all the time. I've checked, cleaned and tightened the battery terminals and charged the battery but that hasn't helped. I'm assuming the alternator has given up (for a couple of days there's been a clanky noise whilst the engine is running too).
I'm far from competent as a mechanic and have little in the way of tools. Would it be more prudent to get a garage to do it, or is it something I might manage alone? I'm in Moreton-in-Marsh in the far north of Gloucestershire, right on the boundary where Glos, Oxon, Warks and Worcs meet, so if anyone knows of a good local place to send me to, please do let me know.
Alternatively, is there anything else I should check/do before committing myself to a new alternator?
Thanks

I may be wrong, don't know the belt setup on the TD4 - but the pulleys delaminate - so could it be that its not turning the belt driving the alternator?

Check battery voltage, should be 12v or more. Start car should be 13.8v or a bit more. If the voltage doesn't increase then likely to be alternator fault. They seem to last about 130k miles then the brushes wear through!

It isn't a job for a novice, esp if you have air con, the compressor is in the way and has to be moved.

Sounds like the alternator, mine lasted about 200k before intermittant flashing of alternator light and then on constantly.
Bushes had worn through slip rings.....
It's not a bad job, serpentine belt and hooking a/c compressor up out of the way are the only awkwards bits, rest is just nuts and bolts, and then re-fitting serpentine belt....... big spanner needed and figuring out where the hell this belt goes now!

Not a bad job to do, just make sure you get the right alternator, 115 amp, 150 amp, 2 pin rectangular plug, 3 pin rectangular plug, or "church door" style plug, something like that. Mine is the 150 amp, first alternator had failed brushes, second had seized bearing. Mine had 2 wire arched plug, but I used 2 wire square plug alternator and joined the wires.

Thanks chaps - I'll do that battery test.
No aircon on my TD4, but what it does have is 196,000+ miles on the clock, so it may well be that the alternator has simply died of old age. I'm not expecting this car to last me much past the summer, so for the sake of economy I'll see about a trip to a breakers yard for a replacement if needs be.
I assume access is all upward from below - might spend Saturday morning on my back, first of all checking out the condition (or maybe even presence - who knows lol) of the belt, then taking it from there. I'll have a mooch around online to see if there's a layout map of the belts, so I know which one I'm looking at. From above I could only see two belts, the upper of which looked okay and felt good, but the lower was out of reach though the very limited view of it I had didn't suggest it was loose or damaged.
Better get on AmazonBay and price up a jack and maybe some axle stands or ramps
I shall keep you apprised of each calamity as I cause it lol.
PS - Any idea of the sizes of spanner I'm likely to need? I think the set I have goes up to about 19mm. My Haynes manual tells me nothing - it doesn't even suggest that the diesel models *have* an alternator! (EDIT - SPANNER SIZE SORTED - SEE NEXT POST)

Looked through some older posts and found the spanner size - 24mm ring spanner flattish (not cranked). I'll see about getting one from somewhere, and have found a decent trolley jack (2T), axle stands (3T each) and rear wheel chocks (handbrake isn't very good) for the sake of extra safety whilst underneath.
If/when I replace the alternator, is it good practice to replace the belt at the same time even if it doesn't look particularly knackered? Also, while I'm under there, is it worth covering the belt/s in a coat of that aerosol belt spray stuff? Are there any other little jobs/checks I could be doing to mitigate future issues while I'm in that area of the engine? I've heard it said that replacing the splash cover once I've finished isn't entirely critical and helps with future oil changes, which I'm planning on doing in a month or two. I never go off-road to any degree - a 1/4 mile muddy lane at walking pace to a field to walk the dog are as off-road as it ever gets for me, especially as my car has no propshaft so is only ever FWD anyway!