The song was written by Harry Wincott.

You can read all about him here

I don't think there was a London Beer called McIntyre's. It was customary to put the word 'entire' after a brewer's name, however.

As in Nalder& Collyer's Entire....entire being a style of Porter or light stout (originally 6.6 abv!)

But it is doubtful whether this has anything to do with anything!

I guess Harry used the name because it fitted the song and rhymed with fire!

Best wishes,

Peter