The judge leading the public inquiry into the Edinburgh trams debacle has said key individuals have refused “point blank” to cooperate.

In an interview with BBC Scotland, Lord Hardie (pictured) said the investigation would be tough.

The Scottish government said in November that the inquiry was to be given the power to make witnesses participate.

Lord Hardie said: “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.

“One of the functions of the system that we are procuring is that it will sort out the documents into various orders and it will be able to identify gaps, for instance in an email trail.

“We will learn from that if there are indeed gaps.”

It is unknown when the first public hearings will take place or who Lord Hardie will call before him.

Lord Hardie added: “There were consequences that I am aware of for householders, for shopkeepers, for developers not only along the route of the tram but along the diverted routes of traffic.

“I would put out a plea to them now to think about what they are going to say, to get together with like-minded people to present a joint submission to the inquiry at the appropriate time, which will be when we call for evidence.

“If lessons are learned, then the benefit of this inquiry will be that future public procurement contracts will be delivered on time, on budget and as promised.”

The trams began running in May, following six years of disruption and a dispute between the city council and its contractor.

The project cost £776 million, up from the initial budget of £375m and was years late.