Former Ontario premier Dalton McGuinty admitted Tuesday he didn't know the full cost of moving gas plants in Oakville and Mississauga when he made the controversial decision to relocate them.

Speaking before the legislature’s justice committee Tuesday, McGuinty admitted the decision to relocate the plants west of Toronto came later and cost more than he would have liked, but he said relocating them was the right decision, given their proximity to schools and homes.

"We were faced with a circumstance where gas plants were sited right next to schools, condominium towers, family homes and a hospital," he said. "That wasn't right."

The decision to close the power-generating plants become controversial for two reasons. The first was the timing: the Mississauga plant announcement came during the 2011 election campaign; the Oakville decision came a year earlier. Both decisions were made in response to growing opposition in ridings held by Liberal MPPs.

The combined cost of tearing up contracts with the developers was another problem. The cost of moving both plants is now estimated to be more than $585 million, far above the $230 million McGuinty and the Liberals had been claiming.

During his testimony on Tuesday, McGuinty's clashed with Progressive Conservative MPP Vic Fedeli, especially when McGuinty insisted the $40-million figure the Liberals had been using as the cost of cancelling the Oakville plant came from the Ontario Power Authority. It was recently estimated that moving the plant will likely cost more than $300 million. An auditor's report on the Oakville relocation is due this summer.

'I don't believe your answer'

The auditor general has estimated the cost of cancelling the Mississauga gas plant during will be at least $275 million, $85 million more than McGuinty or the Liberals were admitting during his time as premier.

"You keep saying that I'm not giving you an answer," complained McGuinty, "Perhaps you don't like the answer."

"No, no, I don't believe the answer," said Fedeli. "To be perfectly frank, I don't believe your answer."

McGuinty also said he took responsibility for relocating both plants, which he said was the right thing to do because of their proximity to schools and residences.

"We got 17 gas plants more or less right, but we got two very, very wrong," he said. "There was a strong sense that my government had made a mistake in choosing those locations," said McGuinty.

Prorogued legislature

Tory MPP John Yakabuski questioned McGuinty's stated reason for moving the plants, pointing out that any potential environmental issues would have been known when the sites were chosen more than five years earlier.

"In both these cases, you were presented with the polling that said 'we’ve got to shut these down,'" said Yakabuski.

McGuinty had blamed the heated debate over the gas plant cancellations last fall when he suddenly prorogued the legislature and announced his resignation as premier.

Both opposition parties say Kathleen Wynne, who succeeded McGuinty in January, wasn't as forthcoming as she could have been when she testified about the gas plants last week.

Wynne has said she was not involved in the government’s decision to scrap either plant.