What is the central and most important irony in "The Rocking-Horse Winner"?

To my mind, at least, the central irony that creates the
conflict that runs through the whole story is introduced to us in the first paragraph
when we meet Paul's mother. Note how the text presents
her:

She had
bonny children, yet she felt they had been thrust upon her, and she could not love
them... Everybody else said of her: "She is such a good mother. She adores her
children." Only she herself, and her children themselves, knew it was not so. They read
it in each other's eyes.

The
irony of this passage is that the mother appears to love her children, and gives every
visible proof of her affections through her actions, but this cannot prevent the reality
of her heart "turning hard" whenever she is with them. It is this lack of love that
drives Paul to go to such supernatural lengths to gain money to make his mother happy,
and therefore gain her genuine affection. Note how this irony is referred to again at
the end of the story by Uncle Oscar, her brother:

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"My God, Hester, you're eight-odd thousand to
the good, and a poor devil of a son to the bad. But, poor devil, poor devil, he's best
gone out of a life where he rides his rocking horse to find a
winner."

Note the criticism
that is implicit in this remark. Paul is "best gone" from a life where he is forced to
go to such lengths to make his mother notice him. Although Hester has what she wanted,
she has only gained it through losing her son.