The leaders of the Progressive Conservatives and the Canadian Alliance made it official on Thursday. "We are announcing today," said Tory leader Peter MacKay, "an agreement in principle for the union of our parties, and a reunion of conservatives across Canada."

MacKay won his party's leadership just four months ago after pledging in writing not to merge with the Alliance. But late Wednesday night, he signed an agreement to do just that.

Stephen Harper, the Canadian Alliance leader, was also a reluctant convert to the merger. He once pledged he'd have no truck or trade with the Tories. But when he appeared before reporters in the National Press Theatre in Ottawa his attitude had changed. "Some people know that I don't get excited too often, but I had difficulty sleeping last night," he said.

What the leaders have agreed to is a proposal to merge. Both parties must ratify the deal by Dec. 12. If approved, there will be a membership drive for the new party, all old cards will be void.

A new leader will be chosen late in March with equal votes coming from each riding. Existing MPs will not be automatic candidates; riding contests will be open, and an interim joint council will write a new first constitution.

Since the timeline is so short there are no plans for a founding policy convention before an expected spring election. MacKay says the new party will have to be ready for a quick election. He says Paul Martin, who is expected to become Liberal leader next month, may call a spring election, "but we have no control over that."

With the broad strokes of policy already in the deal, including the equality of French and English and progressive social policies, it suggests the Tories have come out the winner in policy field, in the process of electing a new leader, and even the new name, which will be the Conservative Party of Canada.

Harper agrees that the Canadian Alliance made "significant concessions." "I am not going to deny that," he said. But, Harper said, the governing Liberals would no longer be able stand for re-election with a divided opposition. "Our swords will henceforth be pointed at the Liberals, not at each other."

The job now is to convince their two parties about the wisdom of becoming one again after 16 years of separation.