An elections watchdog is set on a collision course with Deputy Prime Minister Nick Clegg after he dismissed calls for a law change to ensure last-minute voters are not turned away.
The Electoral Commission said it was "disappointed" the Government had ignored its call for legislation to prevent a repeat of angry scenes during May's general election.
It also aired fears that town hall budget cuts could affect the smooth running of the referendum on changing the voting system due for May 5 next year.
At least 1,200 people were still queuing in 16 constituencies when polls officially closed at 10pm, meaning they could not cast their ballot.
The Commission fears the same could happen when the whole country goes to the polls again in May 2011 to decide whether to move to the Alternative Vote system for future general elections.
But ministers refused to meet its call to introduce a legal right to vote for anyone who arrives before 10pm as part of the Bill paving the way for the poll - which has been approved by MPs.
On Wednesday Mr Clegg told the Commons that legislation was not the answer: "The problem was a lack of resources, the problem was poor organisation by the returning officer. That's what we need to address - not always simply reach for the statute book," he said.
Now the watchdog is waiting to see whether peers will seek to make the change when it passes to the upper House but warns that time is running out.
It wants all measures in place for the referendum - which is controversially being held alongside local and devolved elections - at least six months in advance.
In an update on the chances of a smooth-running referendum, Commission chair Jenny Watson said that while "enough progress" had been made, it remained a "major challenge".