The last survivor of the 1914 Christmas truce, a private called Bertie Felstead, only died in August 2001 - here's a piece about him and about the truce.

And one of the things it mentions is that there was a similar partial Christmas truce at Christmas 1915 :

"Many years later, talking about his own experience of a similar truce in 1915, Felstead recalled that the sound of German soldiers singing Silent Night, barely 100 yards away, encouraged the British to respond with Good King Wenceslas. The following day, there was an impromptu kick-about with a football.

This seasonal fraternisation apparently went on for about half an hour, until brought to an abrupt end by a furious British officer, who ordered his men back to the trenches, telling them. In no uncertain terms, the brutal truth of their situation. Namely that they were there "to kill the Hun, not make friends with him".

...In an interview two years before his death, Felstead made a telling comment which explained why the military authorities reacted so strongly against friendly contact with the enemy. Recalling the carols, sung in the trenches on Christmas Eve, he said: "You couldn't hear each other sing like that without it affecting your feelings for the other side?"

And in fact the first Christmas truce lasted until January 1915, and there were real worries on the part of the commanders on both sides that there might be difficulty in getting the war started again.

That site I linked to for Bernie Felstead is a really fascinating one, with all kind of stuff about the Great War. And it includes the text and a sound file of Mike Harding's song about a "Pals Brigade" - "The Accrington Pals"

Here is the song, because it ought to be on the Mudcat, and links to other sites can fail over time:

Smoky town where they were born,
Down in the valley, smoky little streets.
They were pals from childhood days,
Climbing trees and running through the fields.
And they all played together through the turning of the years,
Sharing their laughter, sharing all their fears.
Seasons saw them growing and
Seasons passing turned them round
With the turning, turning, turning years -
The Accrington Pals.

Schooldays' end the lads all went
To work, some spinning, some weaving in the sheds,
On the land or down the pit,
Working hard to earn their daily bread.
And they all went walking up old Pendle Hill,
On Sundays the larks sang high above the dales.
Little Willie Riley played his mandolin and sang,
They were laughing, they were singing then -
The Accrington Pals.

1916 came the call,
"We need more lads to battle with the Hun.
Lads of Lancashire, heed the call,
With God on our side, the battle will soon be won."
So they all came marching to the beating of the drums,
Down from the fields and factories they come,
Smiling at the girls who
Came to see them on their way.
They were marching, marching, marching away -
The Accrington Pals.

Blue sky shining on a perfect day,
A lark was singing, high above the Somme.
Brothers, pals and fathers lay
Watching that sweet bird sing in the quiet of the dawn.
And they all went walking out towards the howling guns,
Talking and laughing, calmly walking on,
Believing in the lies that
Left them dying in the mud,
And they're lying, lying, lying still -
The Accrington Pals.

Smoky town which heard the news,
Down in the valley, smoky little streets.
Houses quiet and curtains pulled,
All round the town a silent shroud of grief.
And the larks were singing still above old Pendle Hill,
The wind was in the bracken and the sun was shining still.
A lark was singing sweetly as
The evening fell upon the Somme.

(spoken) For Edward Parkinson,
Bobby Henderson, Willie Clegg,
Johnny Molloy, Norman Jones,
Albert Berry, Willie Riley -
(sung) The Accrington Pals.
(drum-roll into brass band arrangement of "The Battle of the Somme")