The information was drawn from the Electoral Register and, according to a report in the Times, is though to include addresses, telephone numbers and likely voting intentions, although the Tory party did not confirm this.
A spokesman for the Tories told the newspaper that the journalist to whom the information was sent and the local newspaper to which he forwarded the email had both given undertakings that the information had been destroyed. The party is now investigating the mistake.
However, it comes as the Tory party faces the real prospect of winning the by-election in Crewe & Nantwich, the formerly safe Labour seat held by longstanding MP Gwyneth Dunwoody, until her death earlier this year.
Polls show that the Conservative party are in the lead ahead of the vote on Thursday, and no doubt the Labour party will be hoping that the data blunder will go some way to countering the bad feeling among voters caused by the 10p tax-rate abolition and general economic malaise.
However, Labour has been playing up class politics in the campaign to embarrass the Tories and their multimillionaire candidate Edward Timpson, of the shoe repair store empire.
Labour's candidate is Dunwoody's daughter Tamsin.