The following poem appears to be the original text:

                                BLANK FIRE

I landed in London and straight away rode
Direct to Headquarters in Horseferry Road;
A bucksheesh Lance Corporal said, "Pardon me, please,
You have dust on your tunic and dirt on your knees,
You look such a sight that people will laugh,                                 
Said the cold-footed --- of Horseferry Staff.

"Your hat should be turned up at the side like mine
Your boots, I might state, are in want of a shine,
Your puttees are falling away from your calf;
Said the cold-footed --- of Horseferry Staff.

The soldier gave him a murderous glance,
"Remember I'm just home from the trenches in France,
Where shrapnel is flying and comforts are few,
Where the soldiers are dying for --- like you.

"You bully the soldier you meet in the street,
And tell them you suffer from frost-bitten feet,
While your mates in the trenches fight on behalf
Of you cold-footed --- of Horseferry Staff.

"You speak to a soldier you cold-footed cur.
What of your Mother, did it ever strike her,
That her son was a waster and afraid of a strafe,
Who hangs on to his job at Horseferry Staff."

- Lieutenant W. T. Barnes

Australian War Memorial, 1918 Australians in France [http://www.awm.gov.au/exhibitions/1918/soldier/superiors.asp] (as of May 1, 2010).

John Vereker, Viscount Gort, was never stationed in Horseferry Road, the WW1 headquarters of the Australian Imperial Forces (who did not arrive in France till 1916). Nor were Australian units in France in 1939-40, when Gort commanded all British forces. A British soldier presumably added the lines about Gort, either in 1939-40, or else earlier when Gort commanded of the 4th and later the 1st Battalion of the Grenadier Guards of the British Army, 1917-1918.

In WW1, Gort was not well known beyond his own British units. In 1940, however, he was commander of an entire army.