"Tom, who has taken, unflatteringly, to calling himself a hag-fag"
Fag hag
Fag hag
Creative Commons AttributionFag hag - Credit: Till Krech

A fag hag is a woman who spends most of her time in the company of gay men.  As Tom spends most of his time with Shazza, Jude and Bridget, they are the hags he is referring to when reversing the term.