The chair of the inquiry into the Edinburgh trams project said he is determined to get answers after it emerged key figures refused to co-operate.

Lord Hardie said lessons must be learned from the flawed planning and construction programme which saw the trams rolled out in May years late and significantly over budget.

It was announced last month that the public inquiry has been awarded statutory powers to allow the senior judge to compel witnesses to participate.

The Scottish Government took action after some of those involved in the project refused "point-blank" to co-operate, Lord Hardie said.

He told BBC Scotland: "Our preliminary investigations, contacting people who we thought might be of assistance, threw up the problem.

"Some people refused point blank to co-operate, others just didn't answer letters.

"It became clear to me that if that persisted then the whole process could be frustrated and certainly take a period of time that was unacceptable to me."

The official Edinburgh Tram Inquiry website was launched today at www.edinburghtraminquiry.org.

A request will be made later for evidence from members of the public and businesses affected by the construction delays, and the fact that original plans for a more extensive line were curbed.

Lord Hardie said: "As chairman, I am determined to ensure we conduct a robust, timely and effective inquiry, and one that will get the answers the public demands to ensure lessons are learnt for future major infrastructure projects."

The trams began operating on May 31 after six years of disruption and a long-running dispute between Edinburgh City Council and contractors.

The eventual cost of £776 million was more than double the sum earmarked for the project by the previous Labour-led administration.

The trams, used by 1.5 million people in the 100 days after their completion, run from Edinburgh Airport to York Place.