Britain's Conservative Party is struggling with its voter-targeting software, while the opposition Labour Party believes its technology will help it win in crucial marginal constituencies, a report suggest.

The report, in Newsweek magazine, cites sources in both camps highlighting the significant differences "between the use of technology to effectively target swing voters - an area into which the parties have funnelled millions of pounds".

The election is on a knife-edge with just under three weeks until polling day, and both major parties are struggling against a surge in support for the United Kingdom Independence Party (Ukip) and the Scottish National Party (SNP).

While Labour is using a system called Contact Creator, Newsweek says the Tories have been struggling with first its Merlin system and then its Votesource software.

The magazine quoted former Tory candidate and author Dr Anthony Ridge-Newman, who said: "There is a latent culture of grumpiness in [local Conservative] associations - because of centrally imposed initiatives.

"Merlin is a good example of that, as is Votesource, because the party is poorly organised in its approach. It's not necessarily the technologies - it's how late in the day they have been implemented."