Forget Worcester Woman or Mondeo Man, the classic swing voter courted so assiduously by the parties at previous elections.

The UK is changing so fast that a diverse new group of “kingmaker seats” will decide whether David Cameron or Ed Miliband is prime minister next month.

The seats are both urban and rural; in the north and the south; populated by large numbers of young and old; by socially conservative and liberal voters who are both white and diverse.

Five of the 12 weather vane seats are among the most ethnically diverse in the country, according to a study by British Future. They include Ealing Central and Acton in London, where Angie Bray is defending the seat she gained for the Conservatives from Labour in 2010, which has 36,745 black and ethnic minority voters.

British Future concludes that the parties need to widen their focus: “A governing party needs to find common ground between the voters of Harrow East, where over a quarter of voters are Hindu, and 97 per cent white Cannock Chase, where Ukip is polling a third of the vote.”

The 12 “kingmaker” seats were selected after British Future studied constituency polling by Lord Ashcroft, the Tories’ former deputy chairman, and bookmakers’ odds offered by Ladbrokes.