North Wales Chief Constable Richard Brunstrom said that the campaign, which is running in marginal constituencies, used incomparable data to show that crime rates were soaring.
He told Channel 4 News yesterday: "This misleading advert quite improperly seeks to stir up fear of rising crime when it is a well-established fact that crime has been falling for years, both locally and nationally."
It was also reported that six other chief constables held the same view, and the claim has been supported by the Association of Chief Police Officers, which issued a statement saying: "If we wanted to increase fear of crime, the select use of statistics can help in doing that."
With the May 5 general election due to be announced on Monday, the battle for voters is hotting up and the Conservatives' advertising has already stirred controversy -- most recently with an advertisement saying that there is one law for travellers and another for everyone else.
Labour has also been in trouble over two advertisements it had proposed running, which were seen by some as being anti-Semitic.
The main thrust of Labour's advertising so far this year is reminding people of the strong economy and of Tory leader Michael Howard's connection to the Thatcher government.
The Tories are fighting back with a populist campaign looking at issues such as immigration, hospital cleanliness and education, all with the strapline "Are you thinking what we're thinking?".
Earlier this week, it was revealed that Conservative party officials had emailed broadcasters, asking them not to use the word "Tories" and instead to call them Conservatives.
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