The words as printed in Graeme's book 'Songscapes' are as follows:

v.1 The summer's passed into the winter
    The tired old sun is late to rise
    Frosty etchings on my window
    The streams are silent under the ice
    The trees are stark, the sky is clouded
    Hard the clay beneath my feet
    The fields with rook and crow are crowded
    The year is all but over.
    Goodbye old year you're now behind me
    I'll often think of you and smile
    For all in all you tret(sic) me kindly
    You brought me love though just for a while.
   
v.2 Your spring was sweet, your spring was gentle
    The winds of March and April's rain
    Soothed my brow when I was troubled
    And I was boyish once again
    I gave my love a lapwing's feather
    And she kissed me in return
    Beside the burn we walked together
    And the year was youthful then.
    Goodby old year.....

v.3 Come the summer, such a summer,
    Sun filled days and love filled nights.
    Speckled shadows among the willows
    Every hour a new delight.
    Oh such joy when I was with her
    Arm in arm and hand in hand
    But golden days dulled into silver
    For now the year was ageing.
    Goodbye old year.....

v.4 Came the autumn, sad, sad autumn
    When pale mist hung above the corn
    In my heart a chill was creeping
    A warning of the coming storm
    Oh such loving I did give her
    But then she turned and went her way
    And as the leaves began to wither
    I saw the year was dying.
    Goodbye old year.....

v.5 Now the winter, bleak December
    At my door a swirling squall
    Flickering flames and glowing embers
    Shadows dancing on the wall
    In my mind I hear her laughter
    Faint upon the sighing wind
    I think of her, my hear beats faster
    But now the year has passed and gone
    Goodbye old year you're now behind me
    You've gone your way I'll go mine
    Both joy and sadness you've left inside me
    You brought me love though for a short time.

This is the closest you are likely to get to an 'official' version. What Martyn sings will almost certainly vary from this, and probably from performance to performance. Such is the folk process. Don't worry too much about it. The important thing is to sing the song.