Pencil Skirt Lyrics

Lyric discussion by Prisoner.I.Was 

Cover art for Pencil Skirt lyrics by Pulp

I think this song is about a man sleeping with an older, married woman. The 'pencil skirt' seems to suggest an older, more sophisticated person than she. She sleeps with him, even though she knows it's wrong, but it is the wrongness of it all that gets her lover off.