I know this as the May Day Carol. My version has dropped several verses and has just three :-

I've been a-wandering all of the night
and the best part of the day,
and when I come back home again
I will bring you a branch of may.

In my pocket I have a purse
tied up with a silver string.
All that it needs is a little silver
to line it well within.

My song is done, I must be gone,
I can no longer stay.
God ble3ss youall both greatand small
and bring you a joyful May.

The first verse given above (Remember us poor Mayers) and the "I/we 've been a-wandering" varse are also the first two of the Furry Day Carol, while the "Life of a man" and "The moon shines bright" verses have been borrowed from the Bellman's Song. In the version I have of the Bellman's Song, verses 1 and 6 are :-

The moon shines bright and the stars give a light
a little before it was day.
Our Lord our God he called on us
and bid us awake and pray.

The life of a man is but a span
and cut down in its flower :
we are here today and tomorrow are gone -
the creatures of an hour.

The Bellman's Song is a Passion Carol, so would have been sung around the same time as the May Day and Furry Day carols. Of course, there are different tunes for each.

The custom of letting children sing for pennies from door to door, while holding sprigs of may (whitethorn, not blackthorn as I understand, as the black was unlucky) was once universal throughout southern England and perhaps further. Twenty years ago, an old lady wrote to a local magazine to say she remembered doing it as a child in north-east Somerset.