Lib Dem Donald Gorrie, a fierce critic of his party's coalition deal with Labour, and Margo MacDonald of the Scottish National Party say the planned new building at Holyrood in Edinburgh is already hugely over budget.

Donald Gorrie: Project is over budget

They also attack what they say has been a lack of consultation over the parliament's final home, due for completion in 2001, accusing the government of resorting to "ministerial diktat".

The pair say their motion demanding that the parliament building be made an "all-party issue, not a party or government issue" is attracting support from MSPs.

Mr Gorrie said the total cost of the new building's construction, and temporary use of the Church of Scotland Assembly Hall and offices until the building is complete, currently stands at £113m.

The Scottish Office, said Mr Gorrie, had the option of using the Royal High School building at Calton Hill and government offices at St Andrew's House, all for under £50m.

"Instead, it chose a new site at Holyrood, where the building will cost at least £83.6m plus the cost of roadworks not yet calculated.

"The renovation of St Andrew's House, which was included in the costing of the Calton Hill proposal, but is a necessary add-on for the Holyrood scheme is costing £20m."

Temporary use

Mr Gorrie said temporary use of the Assembly Hall on the Mound is £7.7m.

"So the total cost of this choice is not the £50m promised but £113m and rising."

He added: "This is an example of bad politics at its worst. It was a bad decision by ministerial diktat, against the great weight of informed opinion and with no discussion by Parliament."

Margo MacDonald, a Lothians region MSP, said the Parliament may have to consider another site because the architect commissioned for the Holyrood building, Enric Miralles, appears to have altered the agreed design.

The parliament's present home on The Mound

She said: "From what we know of the amended plan for the debating chamber at Holyrood, the architect has strayed from the specification for a horseshoe-shaped chamber such as the one on the Mound, or has so altered the design as to negate the contractual obligations agreed between himself and the Scottish Office."

A Scottish Office spokesman said MSPs would be entitled to take on issues surrounding the parliament site and could ultimately decide to go elsewhere if they wished to do so.

But he pointed out that current leasing arrangements, and in particular those with the Church of Scotland over the temporary home of the parliament, would have to be taken into account.

And a government source expressed surprise at the opposition to the site, given the establishment of an all-party steering group on the parliament prior to the elections.