Tory Leader Peter MacKay slammed MP Scott Brison's jump to the Liberal party Wednesday, saying it's a cynical and manipulative move to advance his career.

MacKay said Brison voted for and supported the ratification of the Alliance-Tory merger.

"It's really quite irreconcilable what he has done today," MacKay said. "What's the motivation?"

Saying the Liberals better reflect his personal values, Brison said Wednesday he was leaving the Progressive Conservatives to join a Paul Martin government. Martin made the announcement at an Ottawa news conference with the Nova Scotia MP.

MacKay said Brison failed to show up at caucus Tuesday and he only heard about his defection Wednesday morning.

"That speaks volumes," MacKay said.

MacKay said he's received calls from people in Brison's constituency "and they're calling it what it is, a completely cynical manipulative move by Mr. Brison to enhance his own personal career."

Brison made the decision to cross the floor following two conversations with Martin, who becomes prime minister on Friday.

Brison received a standing ovation at a Liberal caucus meeting Wednesday.

A member of the PCs for more than 25 years, Brison said he struggled with the merger between the Progressive Conservatives and Canadian Alliance. He had said he would endorse the new party if it adopted progressive policies.

"The PC party the party I grew up in no longer exists," said Brison.

He says the Liberal party better reflects his personal values and the values of his constituents.

"There is great angst as to the direction of the new Conservative Party," said Brison.

Martin welcomed Brison to the Liberal caucus, saying he will make a "tremendous addition" to the party.

Brison, who is openly gay, has told friends he expects the new Conservative Party will have problems with intolerant members of Parliament. He says he wants to avoid becoming what he calls a poster boy for gay issues.

"This nonsense about the party leaving him makes no sense," MacKay said. "This is about Scott Brison himself. This isn't about the political future of this new conservative movement. This is about his own future."

As a Liberal, Brison has decided he would be able to focus on economics and tax policy.

He has also said he believes Martin will make an exceptional prime minister.

An MP from the Bloc Qubcois recently joined the Liberals. The Liberals say the defections illustrate Martin's drawing power to what they like to call a "big tent" party.

The Conservatives' failure to keep Brison is political ammunition for the Liberals, who have called the new party little more than the Canadian Alliance with a fresh logo.

Earlier in the year, Brison ran against MacKay for the leadership of the Progressive Conservatives.