Hi Edd, does sound like alternator. (I assume that you have the ignition light on permanently whilst engine running and that you have checked auxilliary belt ok)
I changed mine last year, but I never did a guide as there didn't seem to be much interest. Also, whilst i was wrestling with the job I didn't manage to take any pictures.
The sequence I used (from memory) was something like:
Disconnect battery. (If you do this within 10 seconds of ignition off it stops the alarm sounding!)
Unbolt bagpipes and carefully lift up on to plenum (leaving all vacuum pipes etc connected). Having carefully noted the route for the auxilliary belt, remove from the alternator pulley. (Use a socket on the tensioner to remove tension).
Jack up front of car and safely secure on axle stands
Remove sump guard/cover
Working from below, (use every spanner/socket/bendy extension in the toolbox trying to gain access

) undo the bolts securing the alternator.
Once the alternator is free, and working from above the engine, move and tilt alternator forward and remove electrical connections and finally pull unit forward and up to remove.
Refitting is, as they say, reversal of the removal instructions. On a final note, It was so difficult to get at the rear nut that I 'super glued' it to the rear mounting lug off the alternator. The glue held long enough to get the bolt started and made the job much easier.
The job was not technically difficult but was extremely difficult because of poor access to the lower rear nut as the engine mount was in the way.
Hope this is of some use to you. Hope it goes well for you