THE SNP's special conference next month will be given a completely free vote on a measure to get more women into the Scottish Parliament, to the dismay of supporters of gender equality who had hoped the leadership would endorse the plan.

It is official party policy to use the regional lists of additional MSPs to bring about gender balance, and a mechanism for doing this will be put to the special conference in Perth.

This would involve party members electing separate male and female lists in each region and then ''zipping'' these - alternating between the two to create the final ranking for the final list which goes before the electorate at the Scottish Parliament election.

With the SNP likely to do better out of the additional members lists than in first-past-the-post constituency seats, zipping is the only measure being considered to boost the number of women making it to Holyrood.

However, an amendment from the party's youth wing, Young Scots for Independence, and Edinburgh West Constituency Association, calls for the mechanism to be scrapped.

The party's national executive committee has put its name to both the zipping clause and the amendment deleting it, in order to signify that it a completely free vote, with no leadership line.

However gender equality campaigners believe this is a cop-out and say the executive should have put its weight behind the mechanism because it promotes official party policy. ''This is simply outrageous,'' said Hilary Brown of the SNP Women's Forum.

''Women in the party and beyond throughout Scotland would have hoped for better. It is more than disappointing that the leadership could not wholeheartedly support this. I wonder what message this sends out?

''If we fail to get the zip in the lists we will be left with nothing to ensure an acceptable number of women MSPs. I am still confident that we can win this debate, but it is disappointing that we have not had stronger support from the executive.''

However, senior party sources indicated that they thought any hint of fixes or a strong leadership line could have been counter-productive.

Unveiling the conference agenda, National Secretary Colin Campbell, said that, wherever there were choices, the NEC had endorsed all viewpoints in order to signal complete even-handedness.

For example, in terms of electing and ranking the regional lists, there are three choices. One is one-member, one-vote with a postal ballot of all party members in a region.

Another is to elect delegates to make the selection, with the bigger branches receiving proportionately more delegates. The third would give branches equal numbers of delegates regardless of size.

Party chief executive Michael Russell said: ''Compared to the London-based parties, the SNP's process is the most democratic, which sets a marker for our commitment to an equally open and accessible system of government in the Scottish Parliament.''