The true price tag of cancelling two gas plants in Oakville and Mississauga is closer to $828 million, more than three times what the governing Liberals have said taxpayers are on the hook for, an independent energy expert said Wednesday.

The cost of the Oakville plant alone, which was scrapped in 2010, is roughly $638 million, not $40 million as the Liberals have said, Bruce Sharp told a legislative committee looking into the party's decisions to cancel plants in both cities.

Relocating the plant will cost $40 million, but there are additional costs, said Sharp, a mechanical engineer who says he has 25 years of experience in Ontario's energy sector. Sharp who works for Aegent Energy Advisors but was appearing before the committee as an independent expert.

"Costs quoted of $40 million was low," he testified Wednesday. "So I felt the whole subject deserved some attention."

Sharp estimated delivery and management costs of $313 million and transmission costs of $359 million.

"There are so many people making money in so many different ways in the sector, that when something goes wrong, no one wants to talk about it," he told the committee.

Sharp agreed with the Liberal estimate that the cost of relocating the other plant in Mississauga will be about $190 million.

Premier says she's unaware of extra costs

"On the subject of politics, I would just say that we're sitting here today because of the siren call of political intervention and we really need to get away from that political intervention and swear a blood oath to not meddle in electricity policy in Ontario," Sharp said.

The testimony Wednesday fuelled opposition claims that the costs of cancelling the two plants far more than the $230 million the governing Liberals have said.

But Premier Kathleen Wynne said she did not know about any additional costs related to the cancellation of the plant in Oakville.

"I've been very clear that getting all of the information into the public realm is what needs to happen, that's why we moved to have the mandate of the committee broadened," she said.

"I've been very clear about the information that I have been given, so the numbers that I've talked about are the numbers that I knew."

The NDP and Conservatives have accused the Liberals of relocating the Oakville gas plant and then the Mississauga plant during the tail end of the 2011 election campaign to save Liberal seats in the face of local opposition to the projects.

Liberals must 'come clean', NDP says

Both parties have insisted the Liberals knew the cancellation would cost much more than they let on.

"We had a credible witness this morning who made it clear we were looking at costs in the hundreds of milions of dollars. Not $40 million," said NDP critic Peter Tabuns. "The Liberal government has to come clean on the cost of Oakville, it has to start being open and honest about the scale of the problem that we're facing here."

But Bob Delaney, MPP for Mississauga-Streetsville and parliamentary assistant to the energy minister, was skeptical of Sharp's testimony.

He told reporters it was Sharp's personal opinion based on "taking a few figures and making extrapolations" and "plugging them into a formula and a spreadsheet."

"He didn't produce a study or a clear compelling, quantitative peer-reviewed analysis on which we could base the cost of the relocation of these two plants," he said.