The power station in question has already been removed from the project near the Mugga Lane tip.

The Liberals tried to put the controversial data centre project back on the agenda yesterday, the Assembly's last sitting day before October's election.

Opposition Leader Zed Seselja said he had documents that proved ActewAGL had been prepared to construct a data centre without an accompanying power station. But the Government pressured the company to modify its plans to include a ''peaking'' power station.

''This power station was a requirement of the Government: it wasn't something the proponents wanted and this is a new part of the story that we weren't aware of,'' he said.

Mr Seselja accused Chief Minister Jon Stanhope of having lied to the public over the controversial issue and said the Government he led was losing credibility.

ActewAGL chief Michael Costello rejected Mr Seselja's claims outright.

''I think it's a pity they didn't ring me and ask me, because I would have told them it was completely untrue,'' he said.

''We have always been, and we remain, completely committed to building a gas-fired peaking power plant here in the ACT. Far from having pressure put on us, we're the ones pushing the issue.''

Liberal MLAs attacked the Government over the issue in question time yesterday.

Mr Stanhope said the documents did not support Mr Seselja's case ''one iota'' and showed the Opposition was desperate to score political points.

''Would you believe Michael Costello or would you believe Zed Seselja, the struggling, frazzled, inexperienced ... Leader of the Opposition?'' he asked.

A consortium led by ActewAGL plans to build a $1billion gas-fired power station and data centre in Tuggeranong near the Mugga Lane tip.