The electoral register for Brighton and Hove is due to be published today (Monday 1 December).
It is the first to have been compiled since the law changed to bring in individual electoral registration (IER).
Until this year one person in each property – nominally the head of the household – registered everyone at that address.
Recent figures released by Brighton and Hove City Council suggest that the number of voters on the electoral register, or electoral roll, has fallen since IER came into force in June.
In response to a freedom of information request the council said: “On 1 May 2014 there were 209,766 people registered to vote in Brighton and Hove.
“On 1 September 2014 there were 208,415 people registered to vote in Brighton and Hove.”
The council said: “There is still time to register and be eligible to vote in the 2015 general election.
“Residents are urged to register as soon as possible to ensure they are added to the rolling register, which is held on a database and used to generate the poll cards for voters.
“The rolling register records can be updated until (Monday) 20 April 2015.
“Residents are advised to sign up as soon as possible to be sure of inclusion.”
The council added: “If you are unsure as to whether you are registered, please contact Brighton and Hove City Council’s Electoral Services office on 01273 291999 or email email@example.com.”
Among the groups most affected by the new system are students and young people.
Traditionally a lower proportion of students and young people register to vote than other demographic groups.
Even so, the student vote was credited with helping Caroline Lucas to become the first Green MP when she won Brighton Pavilion in 2010.
And students were believed to have helped the Greens to become the biggest party on the council a year later.
The importance of the student vote under the new system is the subject of a think-tank report published today.
The Higher Education Policy Institute report said that students could help Caroline Lucas keep her seat but they could swing neighbouring Brighton Kemptown, held by Simon Kirby, from Conservative to Labour.
The report bases some of its assumptions on national opinion polls.