The last chapters in Australia’s century long battle to decriminalise abortion are being played out in the NSW Upper House this week.

It is ironic that last week, the Herald’s morning newsletter in its "On this Day" slot featured a photo from September 12, 1991. It depicts a walkout by 13 women members of the NSW Legislative Council over Reverend Fred Nile’s anti abortion bill. The boycott left only two women members inside the chamber. The walkout included representatives of all factions and parties – but not Fred Nile’s wife, Elaine.

The most extraordinary thing about the photo is not that the boycott was so strong but that almost 30 years later the same fight is being fought, in the same chamber and sometimes even with the same people. Why is this so?

Beryl Evans, Dorothy Isaacson, Helen Sham-Ho, Meredith Burgman, Patricia Forsyth, Franca Arena, Anne Symonds, Delcia Kite and Judith Walker walk out of the parliamentary debate on the Rev. Fred Nile's anti-abortion bill in 1991. Bruce Milton Miller

As conservative MPs argue for "more time" to discuss the issue, old feminists feel their hackles rising. This issue has been contested in the NSW Parliament since Labor MP George Petersen’s decriminalisation efforts in the early seventies.

The main problem for NSW is that it is quite significantly more religious than other states. The 2016 Census figures show us that NSW is the most Catholic state in Australia (24.1 per cent identified as Catholic compared with, say, South Australia on 17.9 per cent) and is also the most religious generally with 65.3 per cent nominating a religion as opposed to 60 per cent in Australia.

This imbalance is explained by the patterns of early settlement – Irish convicts in the east and Protestant settlers in the west and south compounded by post-war immigration to NSW from Catholic communities in Europe and the Middle East.

The religious imbalance inside the Labor Party was even more pronounced and can be traced back to "The Split" of the fifties when Cardinal Gilroy of Sydney encouraged Catholics to stay in the party and fight the "Communists" while his counterpart in Victoria, Archbishop Mannix urged the Catholics to split from the party and form the Democratic Labor Party.

In the early 1990s there were less than a dozen MPs of non-Catholic background in a NSW Labor caucus of 60-plus.

These circumstances made it hugely difficult for women activists such as MLC Ann Symonds to make headway. Twice in the nineties she led a concerted push to change the legislation and each time it came to a sputtering halt after a straw poll of MPs was conducted. It was quite obvious that the numbers for reform were not there.

During this period Fred Nile introduced half a dozen bills designed to make abortion harder to obtain. These were mostly fended off by government tactics and an unspoken agreement between the two major party leaderships. No one wanted the issue raised. It was too hard.

The preponderance of Catholics in the ALP caucus has fallen over the years but it has been supplemented by a proportional rise of Catholics and fundamentalist Protestants with similar views on abortion in Coalition ranks. We are still a religious state.

It will be a hugely important moment in Australian law reform if the NSW Parliament eventually votes for NSW to become the last state to remove abortion from the criminal code.

Dr Meredith Burgmann was a former Labor president of the NSW Legislative Council and has written about the ALP and abortion in a recent book Choice Words.