Epic tune, there isn't enough John Martyn Tabs on UG so if anyone else has the time; tab 
few out please :D

Tuning
BADGAD

(skip if you happen to be clever enough to know how to tune to that)
Heres how:

Gonna have to drop your 6th string to a B
(you can do this by lowering it until the 10th fret sounds the same as your 5th string open)
And lower your 1st string to a D.
(Lower it until it sounds the same as the 3rd fret of your 2nd string)
The Lower your 2nd string
(Lower it until it sounds the same as your 2nd fret of your 3rd string)

Tuning
BADGAD

verses
-------------0-------------------|
-------------0-------------------|
-------6-----0-------------------|
---5s7---7---0-------------------|
-0-----------2-------------------|
---------------------------------|
              strum abit (x02210@1)------------0--------------------|
------------0--------------------|
-------6----0--------------------|
---5s7---7--4--------------------|
-0----------2--------------------|
------------0--------------------|

chorus

-0-----------------0---------|
-0-----------------0---------|
-0-----------------0---------|
-4-----------------0---------|
-2-----------------5---------|
-0-----------------5---------|

-0-----------------0----------|
-0-----------------0----------|
-0-----------------0----------|
-4-----------------0----------|
-2-----------------5------0h5-|
-0-----------------5--0h5-----|

thats basically all you need for it, obviously strum those chorus chords a bit too, and 
are a bunch of twiddles that John would make up as he played.

hope you enjoy it!
comment if its not right and i'll take another look

Peace
Cammies