The civil engineering contractor was also ordered to pay £100 000 costs after admitting two breaches of Health and Safety regulations . The collapse was described as one of the worst civil engineering disasters in 25 years.
Balfour Beatty's tunnelling adviser, Austrian firm Geoconsult, denied both charges but was found guilty. It was fined £500 000 and ordered to pay £100 000 costs.
Justice Creswell said: "This engineering disaster is a disgrace in that employees and those not employed were exposed to very serious risks to their safety.
"It occurred under the world's busiest airport and close to the Piccadilly Line – 75 m away."
Justice Creswell said Balfour Beatty was more culpable than the engineer for the collapse as it was in overall charge of the operation.
Prosecutor Hugh Carlisle QC said Balfour Beatty had tried to cut costs, with engineers from Geoconsult only occasionally in attendance. He said: "They chose to restrict the input from Geoconsult to keep the price down. They went into it with their eyes open – as businessmen, their intention was of making money."
Carlisle told the court that there had been difficulties on the project from the start, with 133 items corrected by 11 October 1994, when the collapse occurred. He said that cracks had appeared in the tunnel wall months before the disaster, but that "remedial works were not properly planned or supervised and [Balfour Beatty] failed to contact authorities when the collapse was inevitable."
Geoffrey Nice QC, counsel for Balfour Beatty, said the prosecution was "pursuing the case with a zeal that is unseemly". He told Justice Creswell that in a near miss the first reaction should be one of relief.
He said: "In earlier days, people would have thanked the Almighty and counted their blessings a lesson had been learned." But Justice Creswell insisted: "There can be no compromise over public safety."
Nice denied a suggestion that Balfour Beatty had cut its tender price by 10% and noted that Balfour Beatty was not the lowest bidder .
Nice rejected prosecution claims that six engineers should have been on the site at all times and that they should have taken note of warnings from soil tests that suggested the tunnel might collapse.
For Geoconsult, Arthur Marriott QC said the company apologised for the tunnel collapse but noted that it "was not like an earthquake".
He said that repair work on the cladding had been conducted as work progressed. There had been no time when the dangers had become critical, and prosecution allegations that warnings of a collapse had been ignored were "coloured by hindsight".
He also claimed that the Health and Safety Executive had chased the two companies in an opportunistic way and, for that reason, Geoconsult was seeking to have its expenses paid by the HSE.
Much of the case concerned Balfour Beatty's use of the New Austrian Tunnelling Method, and a new scheme of "self-certification".
As a result of the collapse, use of the tunnelling method was suspended on the Jubilee Line Extension before being given the all-clear by the HSE.
However, the six month delay to the JLE added hundreds of millions of pounds to its cost. London Underground has already had to pay money out to contractors delayed by the ban on the tunnelling method, and some outstanding claims are still unsettled.
No one was injured in the collapse, which caused a major alert at the airport and cost tens of millions of pounds.
