This is the version that I learnt with Durham University Treasure Trap (a UK LARP group)

I think it's a very slightly different tune to some of the ones kicking about, because a lot of the words posted about don't quite scan with the tune I know.

There were three jolly coachmen sat in an English tavern (x2)
And they decided (x3)
To have another flagon.

CHORUS:
Come landlord fill my flowing bowl until it doth flow over (x2)
For tonight we'll very merry be (x3)
Tomorrow we'll be sober.

Here's to the man who drinks small beer and goes to bed quite sober (x2)
Falls as the leaves do fall (x3)
He'll die before October.

[chorus]

Here's to the man who drinks strong ale and goes to bed quite mellow (x2)
Lives as he ought to live (x3)
For he's a jolly good fellow.

[chorus]

Here's to the maid who steals a kiss and runs back to her mother (x2)
She's a very foolish girl (x3)
She'll never get another.

[chorus]

Here's to the maid who steals a kiss and comes back for another (x2)
She's a boon to all mankind (x3)
And soon she'll be a mother.

[chorus]

If I had a thousand bricks I'd build my chimney higher (x2)
For to stop the neighbour's cat (x3)
From pissing on my fire

[chorus]

Now come into the garden green,and don't be so particular (x2)
If the grass is cold and damp,(x3)
We'll do it perpendicular.

[chorus]

Come landlord fill my flowing bowl until it doth flow over (x2)
For tonight we'll very merry be (x3)
(slow) Tomorrow we'll be hung over!

~Iasus (Armourer, DUTT)