"Iron hoof" is slang for horse shoe, but it is also rhyming slang for a four-letter word meaning homosexual which also ends in the letters 'oof'. It has been suggested that the Aintree Iron refers to Brian Epstein, the Beatles' manager.
The aintree iron referred to in the song by the Scaffold was Tommy Smith, a very hard Liverpool football player. They say that Hitler surrendered 4 days after Tommy was born - which goes to show how hard he was!!