The final deadline for legislation which would bring about May's planned referendum on electoral reform is approaching.
The parliamentary voting system and constituencies bill must receive royal assent before parliament rises for its half-term recess on Thursday if the May 5thth vote on electoral reform is to take place as planned.
Labour peers have dug their heels in in recent weeks in a bid to derail the bill. The bill only progressed from its committee stage in the Lords after two major compromises from ministers.
Whips have indicated that if the opposition in the upper House decide to continue their resistance late-night sittings are possible, as they push to complete the legislative process.
Peers will spend Thursday afternoon completing their scrutiny of the legislation in its third reading stage.
The Commons will then consider the amendments to the bill made by the bill on Tuesday - and must decide whether to reject the many changes to the bill peers made. Among them was an amendment requiring the alternative vote referendum to attract a 40% turnout for it to be automatically valid.
If ministers succeed in pushing the bill through parliament the alternative vote referendum could prove a lively contest.
A poll released by the Independent on Sunday newspaper gave the 'yes' camp a ten-point advantage, with 40% of respondents indicating they support AV compared to 30% saying they would reject the proposed shift.