STUDENTS and lecturers hold the key to a “knife-edge” Southampton constituency, a Tory pollster has concluded.

The Itchen seat – held by Labour with a thin majority of just 192 votes – is neck-and-neck with nine months to go to the General Election, a detailed poll found.

Both Labour and the Conservatives are on 34 per cent, with the Liberal Democrats trailing on ten per cent, according to the survey by Lord Ashcroft, a former major Tory donor.

It means David Cameron’s party has enjoyed a slight swing in Itchen since the 2010 election – in sharp contrast to other Labour ultra-marginal seats, where the reverse has happened.

In a blog about his poll – which was taken by 1,000 voters – Lord Ashcroft wrote: “This could point to a very tight race in the city, where the local council elections in May were very closely fought.”

However, the former Conservative deputy chairman suggested Itchen’s “curious demographics” could explain why the result was different to other key seats.

There were “an unusually high proportion of students (most of whom will have been at home elsewhere for the summer vacation) and academics (most of whom will have been in Tuscany. Or Cuba)”.

Lord Ashcroft implied the missing students and academics were more likely to vote Labour next year, adding: “We will see in future rounds of research whether Itchen stays on a knife-edge, or reverts to the general pattern.”

In Itchen journalist and councillor Rowenna Davis will fight to retain the seat held by John Denham, who is standing down after 23 years.

Daily Echo: Rowenna Davis

Labour candidate Rowenna Davis

She will face Royston Smith the leader of the city council’s Conservative opposition, who was narrowly beaten by Mr Denham four years ago.

Daily Echo: Southampton City Council leader Royston Smith and HMS Astute

Conservative candidate Royston Smith

The Tories must win seats such as Itchen if Mr Cameron is to win a Commons majority – while losing it would be a disaster for Labour.

Elsewhere in the county, Lord Ashcroft found that Labour is gaining ground in more Conservative seats, as former Tory voters switch to the UK Independence Party in growing numbers.