There isn't much detail in the article but from what they said on the news last night it sounded like it was to do with a (presumably discontinued) bonus scheme that for no good reason was applied to the jobs men did but not the jobs women did.
They don't yet know how much each woman will be getting. I hope it's decent.
The truly genius aspect of this is that the discriminatory bonus schemes were negotiated by unions, notably the GMB. Singular failure to ensure equal pay, then failure to get it back dated, yet claim victory inseveral cases where men got pay cuts to equalise, then won strike to get pay restored. This is going to be really easy in a period of massive cuts. The question 'equal pay or meals on wheels' has already surfaced. The GMB still managed to set up a sex workers section during this period, in alliance with International Union of Sex Workers - a union which includes pimps employers among its members, a unique achievement in the labour movement. Yay, comrades! Cheers.