Legislation to force general election counts to take place overnight "may not be workable", the elections watchdog has warned.
The Electoral Commission suggested that moves to prevent counts being delayed until the morning after polling day might run into difficulties in practice.
Returning officers also reacted angrily to the move - backed by the Government - insisting that their task was to provide accurate results, not "entertainment".
The row came after Justice Secretary Jack Straw backed a Tory amendment to the Constitutional Reform and Governance Bill requiring vote-counting to start within four hours of the polls closing.
The move comes amid concerns about increasing numbers of local authorities indicating that they do not intend to hold counts until the following morning, potentially delaying an overall result.
But the Electoral Commission and returning officers raised objections to the changes taking place so close to an election. May 6 is currently seen as the most likely date.
An Electoral Commission spokesman said: "We all enjoy election night and understand the desire of parliamentarians and election candidates to know the result as soon as possible after polls close.
"However, returning officers have a responsibility to make sure the results are accurate and accepted. Nothing is more important than that."
He said: "We believe that the new clause as currently drafted may not be workable.
"We do not believe that guidance issued to returning officers could anticipate every circumstance that would justify a delay to the start of the count."
