Previous attempts to gain official member state status has been thwarted because such efforts must pass the security council. Any permanent member can veto any proposal, a long-standing conflict that blocked any UN Security Council progress during the Cold War, since either the US or SU could halt anything, and neither agreed on anything. In this case the US is the primary state objecting to Palestine's recognition of member status as a state, despite the fact that most of the rest of the world affirms their status. Such a measure would undoubtedly pass in the General Assembly, but fail in the Security Council because of the U.S.
However, non-member status can be granted solely by a vote in the General Assembly. France has recently confirmed it will vote in favor. The UK is confirming that it might vote in favor *if* they promise not to seek standing in the International Criminal Court. This deeply troubles me. It is as if the U.K. has announced to the world--"we know that your people have been suffering grave human rights abuses, and that if you are able, you will engage the international criminal justice system to enforce protections for your people. We can't allow that, so we will only vote for your state's recognition if you promise not to avail yourself of protection from human rights abuses."
Palestine likely doesn't need the UK vote to pass the General Assembly, but having it, now that France publicly supports them, is a critical symbolic step in creating a politically stable environment for the Palestinians.
Further complicating this issue, especially for those opposed to Palestinian statehood (primarily the U.S. and Israel), the dominant voice at the table is going to be the US ambassador, Susan Rice. She is currently under severe attack from Republicans for mistaken comments she made about the recent terrorist attack on Benghazi. Ironically, just at the moment that Republicans need her most--to voice opposition to official recognition of Palestine--they are undermining her capacity to argue for the unwelcome U.S. anti-Palestine position (framed synonymously as "pro-Israel", as if these positions were mutually exclusive).