The song's pretty rough (especially live) so there's a little improvising and 
stuff going on each time he plays it; the riff below is right bit to be honest the 
harder and rougher you play this song the better it sounds so go nuts, I guess.

Main Riff
    
    Em                       G
  
E|--------------------------------3-----------------------------|
B|--------------------------------3-----------------------------|
G|--------------------------4--4--4-----------------------------|
D|--2--2--7--7--7--7--7--5--5--5-----10--10--9------------------|
A|--2--2--------------------5--5----------------10--12--12--10--|
E|--0--0--------------------3--3--------------------------------|

To sound right it relies a lot on really hitting the low E when you strike the Em 
and the G; when you play the G for a third time you want to hit the higher strings 
as shown above to make it really sound like the record. With regards to the little 
riff bit you can play pretty fast and loose with these notes and it sounds 'right' 
if you throw in bits of palm muting or hammer on pretty much at random as long as 
the chords and the basic riff notes stay tight.

Main Riff x 4

Verse 1

    D                C
Digging all day and digging all night
    
    Em
To keep my foxhole out of sight

    D                 C
Digging into dinner on a plate on my knees

    Em
The smell of damp webbing in the morning breeze

    D                 C
Fear in my stomach, fear in the sky

    Em
I eat my dinner with a weary eye

    D                 C
After all this it won't be the same

    Em
Messing around on Salisbury Plain

Break: G D C D x 2

Prechorus:

     Em            D
Pick up your feet, fall in, move out

     C                     D
We're going to a party way down South

     Em                    D
Me and the Corporal out on a spree

     C              D
Damned from here to eternity

Chorus:
Em                      Bm          D      C   [Play the chorus chords twice 
I can already taste the blood in my mouth        without vocals and then 
                                                 twice with them]
Em                     Bm       D     C
We're going to a party way down south


Main riff x 4
Verse 2

D                      C
I hate this flat land, there's no cover

Em
for sons and fathers and brothers and lovers

D                       C
I can take the killing, I can take the slaughter

Em
But I don't talk to Sun reporters

D                    C
I never thought that I would be

Em
Fighting fascists in the Southern Sea

D                   C
I saw one today and in his hand

Em
Was a weapon that was made in Birmingham

Break

Prechorus

Chorus

Main Riff x4 

Bridge:
       Em                           G
I wish Kipling and the Captain were here

       D                    C
To record our pursuits for posterity

Em                  G
Me and the Corporal out on a spree

D                C
Damned from here to eternity 

Main Riff x 8

End with Em/D/C/G/strum Em.