Voters in Ipswich are crucial in the battle for Downing Street according to a new report which describes the town as one of 12 “Kingmaker” seats that will determine who becomes the next prime minister.

The “British Future” think tank has produced the list of seats across the country that it sees as vital to either Labour or the Conservatives trying to win the election.

It is based on the history of voting in the seats – but also their demographic make-up and the closeness of the battle indicated by opinion polls and bookmakers odds.

Labour is currently seen as favourite to win all 12 seats – suggesting that Ed Miliband is on his way to Downing Street as leader of the largest single party – but the margins in many, including Ipswich, are still very tight.

The Election Forecast website, which combines opinion poll with bookmakers’ odds, puts Labour on 37% in the seat with the Tories on 36%.

Ladbrokes make Labour 8/11 favourite to win Ipswich with the Conservatives even money.

British Future director Sunder Katwala said his researchers saw Ipswich as important because it was a seat with a comparatively young electorate – a third of the voters are under 34 years old – and yet it was a traditional Labour/Conservative marginal.

He said: “In a real sense it is the Labour/Conservative marginals that will determine who is in Downing Street at the end of this process.

“The battles in Scotland and the West Country involving the SNP and the Liberal Democrats are important, but it is the votes in seats like these that will determine who wins and loses.”

The report says David Cameron would need to take eight of the seats currently tipped to go to Labour to have a viable chance of surviving a confidence vote – putting Mr Miliband in poll position to win the election.

The analysis went down well with both Labour and Conservative campaigns in Ipswich.

Labour candidate David Ellesmere said: “We’ve always known Ipswich is very important. Statistically it is the seat we have to win to make Labour the largest party in the House of Commons and that concentrates everyone’s mind.

“There’s no danger of complacency. We know how important Ipswich is and we’ve got lots of supporters keen to work to get a Labour government back.”

The Conservatives’ Ben Gummer said: “This bears out what I’ve been saying about the importance of Ipswich. The people of Ipswich like an MP who works hard for the town and I hope they recognise what I’ve done.

“The voters of Ipswich are very lucky to have such an important role in choosing the shape of the next government – and in being in a position where one person represents the vast majority of the town in Westminster.”