The song is by Mike Sparks of Herga, based on The Crown pub at Hartest (which has rather more than 13 coins - of varied nature - nailed above the bar and on beams in the pub. There are, however, just 13 names on the WWI war memorial). The story was that they each nailed the coin on the bar for a drink when they returned. ("And every last man Jack, for a pint when he came back, Left a silver florin on the bar" in Mike's song).
Graeme Nights does a slighly different version.

THIRTEEN FLORINS (HARTEST 1915) Mike Sparks

Ch/    Thirteen florins on the bar,
       Their voices echo from afar.
       No one ever said we'd change our golden fields for red
       When we each left a florin on the bar.

The poppies have been laid,
The sermons have been made,
The bold November sun it sinks afar.
And we've bent our heads in prayer
For those we buried there,
Who left these thirteen florins on the bar.                Chorus

We'd sung the harvest hymn,
The nights were drawing in,
We could take a week or two, help win the war.
And every last man Jack,
For a drink when he got back,
Left a silver florin on the bar.

No one thought about the blood
Or the endless seas of mud
Or the sights and sounds that would minds and memories scar.
For when the fighting it was done,
And victory had been won,
It cost these thirteen florins on the bar.                Chorus

Now the decades have rolled past,
Of those who went, well I'm the last,
Their faces throught a haze of years are marred.
If we'd known then what I know now
We'd have stayed to speed the plough
Instead, here's thirteen florins on the bar.                Chorus

The poppies have been laid,
The sermons have been made,
The bold November sun it sinks afar.
And we've bent our heads in prayer
For those we buried there,
Who left these thirteen florins on the bar.                Chorus

Does that help Breezy?

Is there a link to listen to this song anywhere?