Now, more than a century after the Tay Bridge disaster, previously unpublished papers have emerged that show the inquiry into the tragedy was a whitewash.

Disaster struck on the evening of December 28, 1879, when a half-mile section of the two-mile crossing collapsed as a train was crossing from Fife to Dundee. All 12 towers supporting the girders on the 88ft single-track structure fell. Twenty-nine bodies were never recovered.

At the inquiry into the disaster Sir Thomas Bouch, who designed the bridge, was singled out for criticism after it concluded that the structure was ?badly designed, badly constructed and badly maintained?.

However, new evidence shows that repeated warnings about a damaged girder were ignored in the months before the tragedy and that others should also have been brought to account.

Charles McKean, professor of Scottish architectural history at Dundee University, discovered four witness statements in the unpublished papers of Thomas Thorton, the Dundee-based lawyer of the North British Railway company, which show that the damaged girder caused trains to jump or bounce on the track for months before the disaster.

The vital testimony was suppressed by the train company?s lawyer and never presented to the inquiry.

One passenger, John Neilson, said in his witness statement that the ?prancing? of the bridge got progressively worse reaching ?an up and down motion of nine inches in my judgement?.

Another, TD Baxter, said that after one particularly harrowing journey he ?never travelled that way again?, while Provost William Robertson, an engineer, claimed the bounding motion reminded him of a suspension bridge.

Despite having already bought a season ticket, he started using the ferry instead.

Construction and maintenance engineers received a barrage of complaints and were aware of potential problems with the girder, but its safety was never investigated.

According to McKean?s theory, the derailed train carriage crashed into a key coverplate, which weakened and brought down the entire structure.

McKean claims that Thorton undermined the subsequent inquiry by presenting evidence selectively and discouraging witnesses who might damage his employer?s case from coming forward.

The professor says that the eye-witness accounts tally with letters held in the Scottish Records office, which show that a metal girder that had blown off in a storm during the construction of the bridge was repaired and reused, despite having suffered extensive damage.

According to the documents, the builders, who were over-budget and under mounting pressure from the North British Railway to complete the project, decided to cut corners to save time and money.

Bouch, the head engineer of the Tay Bridge Company, was found responsible by the inquiry board, sacked and disgraced.

In his book Battle for the North, to be published this August, McKean says that Bouch was a scapegoat and that if all the evidence had been heard, several other officials would have been implicated.

?At the inquiry there was an agenda,? said McKean, who says North British Railway used its influence to sway the inquiry board. ?They wanted to find a simple scapegoat and so the evidence was tailored to suit. It was about finding a publicly acceptable result. I am now extremely suspicious of modern-day public inquiries.?

While admitting that Bouch was ?far from impressive? and should have shouldered some of the blame, McKean believes his superiors should also have been held to account for cutting corners.

Bill Dow, a retired physics teacher and expert on the Tay Bridge who assisted in McKean?s research, agreed that the company was under a lot of pressure to complete the project and even accepted a bribe to get it up and running in time.

But he disputes McKean?s claim that the inquiry was crooked from the outset.

?In my view this started out as a genuine inquiry and was extremely probing,? he said. ?However when you read the inquiry report you can see that Thorton?s treatment of the head contractor was totally different. It was as if he had on kid gloves.?

Even though the inquiry board comprised some of the most qualified men in the rail industry, Dow says they failed to take the reins. ?The lawyer was in the end allowed to take control of the inquiry.?