Vote counting at next May's council elections could be delayed in many areas until the day after polls close, town hall electoral chiefs have warned.
Council chiefs have warned of delays with vote counting
They have spoken of pressures caused by the new Electoral Administration Act, aimed at curbing postal votes fraud.
Malcolm Dumper, of the Association of Electoral Administrators, said pressure to maintain overnight counting and declarations were "ripe for disaster".
Next year's polls comprise the biggest mid-term voting test for four years.
They will involve all borough, district and unitary councils in England, with the exception of London and eight authorities outside the capital.
With elections for the Scottish Parliament and councils north of the border and the Welsh Assembly, they comprise the biggest mid-term voting test for four years.
Mr Dumper, Southampton's electoral manager, highlighted the impact of the new requirement for checks of signatures accompanying postal ballots with those sent when they were applied for.
He said the number of postal votes being delivered on election day to polling stations and obtained through last-minute Royal Mail delivery arrangements was growing.
"In many rural local government areas, the delivery of these postal votes to count centres could take as much as one to one-and-a-half hours, with the consequence that the processing of these may well not begin until midnight or thereafter."
"The clamour to continue with immediate counting at the close of poll... could well lead to an increasing number of challenges to election results."
The annual drive to update the electoral roll is getting under way this month with letters being sent out to households, seeking confirmation of existing electors and information on new ones.
Under new rules electoral officers are required to make visits in person to addresses from which replies are not received.
The new register comes into force on 1 December.