I don't know the in's and out's (pun intended) of the Civil Partnership scheme... but I assess that it is in no way as binding as a Registry Office marriage.
Marriages are very sticky to dissolve, with issues of divorce, property ownership, child custody, etc (if it all goes wrong, that is).
I would like to know if gay couples would face this problem when splitting up.
Therefore, why should a straight couple have to jump through the hoop of marriage in order to qualify for a quarter. When a gay couple can go through this partnership thing for less hassle.
This makes a mockery of equality in the workplace, but what's new?