Hundreds of thousands of students could be left unable to vote if the government calls an October general election, because there may not be enough time to register them, universities and student unions have warned.

Jeremy Hunt, the chancellor, last week hinted at a possible election October date during questioning by a House of Lords select committee. Universities and student unions were already nervous about the idea of an autumn election, when students are settling into new halls or houses and less likely to be focused on applying to joining the electoral register or acquiring photo ID that will be compatible with the government’s new voter rules.

They also say that an October election – potentially just two or three weeks after freshers’ week in many university towns – would not leave local councils enough time to put many thousands of new student addresses on the electoral register.

Paul Greatrix, registrar of the University of Nottingham, told the Observer that if an election was called for mid-October he did not think the data could be processed in time. “You could easily end up with hundreds of thousands of students being disenfranchised and left without a voice,” he said.

Greatrix said if this happened Nottingham and other universities would launch an urgent information campaign to tell students who were registered at a different university address the year before that they could still vote at a polling station nearby.

Even without an October date there is concern in the sector that new government rules around voting could act to silence students. Since 2015 universities can no longer register their students en masse at the start of the year, as the onus now falls on every individual to register to vote.

With data suggesting that thousands of student voters had fallen off the electoral roll as a result of the new rules, many universities have introduced a system to sign ­students up automatically. This requires every student to tick a box when they enrol at the university at the start of each year if they want their details to be passed on to their local ­council to ­register them to vote. But new research suggests that around 100 universities have yet to do this, leaving it up to students, many of whom will not have voted before and will be living away from home for the first time, to register themselves online.

Nehaal Bajwa, a vice-president of the National Union of Students, said: “The danger is that autumn is such a busy time that many students won’t get around to registering themselves.”

She urged all universities to prioritise introducing automatic enrolment systems “while there is still time”.

The NUS is also warning that many students won’t realise that their student card will not be accepted as proof of identity at polling stations under the new requirement for approved photo ID. Almost 13,000 students have signed up for a free citizen photo ID card, following an NUS campaign, but Bajwa said thousands could still be shut out.

She said: “There was no crisis in voter fraud. This is active voter suppression and we need to make sure all students know it’s happened.”

Nick Hillman, director of the Higher Education Policy Institute (Hepi) think tank, said: “You now need to be pretty organised to apply for ID and register to vote in time, and not many young people on the cusp of a major change in their lives will be.”

A HEPIHepi analysis of the student vote in the 2019 general election showed that Labour did much better in constituencies with lots of students, while the Tories performed “considerably worse”. Labour’s share of the vote was 25% higher in English student seats than in England as a whole, and the Conservatives’ vote share was 25% lower in these seats.

Students have proved ­decisive in some university towns, for instance helping Labour to win both Canterbury and Leeds North West in 2017 and hold them in 2019.

UK general elections tend to take place in May or June. The last general election held in October was in 1974.