John Carson, who led the team behind the Skye Bridge, said condemned the government agency for ditching plans to strengthen part of the bridge five years ago adding that Friday’s closure could be directly linked to that decision.

Mr Carson, former head of one of the country’s biggest engineering firms, Miller Civil Engineering, also warned that commuters face months of disruption as a consequence.

He told The Scotsman: “I fear we’re in for the long haul on this.”

The bridge was shut after fractures were spotted in a load-bearing beam called a “truss end link member” in the north-east tower. The member is part of a linkage system which, as documents from 2010 show, was found to “be significantly overstressed”. A strengthening programme was ordered and then almost immediately cancelled.

Transport Scotland insisted the strengthening programme and last week’s problem are “unrelated”.

But Mr Carson said: “On the one hand they tell us they know about the strengthening issue, but they seem to have ignored it for a long period. Now they are saying that a weld on the pin end which is on the truss end is a big surprise. I don’t think so – this is incompetence on Transport Scotland’s part.”

Meanwhile transport minister Derek Mackay said he remains hopeful the repairs will be completed on time.

Mr Mackay told the BBC that “as it stands” the work should be finished in early January.

He told BBC Radio Scotland’s Good Morning Scotland programme: “As it stands right now, we believe that if we remedy and repair the fault, strengthen that, the bridge should be operational and open to all traffic on completion of the repair as per the timetable that I had outlined over the weekend.”

The Scottish Government believes that the urgent work should be completed by the end of the festive season.

Mr Mackay insisted that the fault was not linked to a drop in finance because of the ending of bridge tolls in 2008.

He said: “This is a fault, that we believe on expert advice, only happened in the last few weeks.

“So on routine inspection, it was identified on Tuesday, expert engineering analysis studied that and inspected it fully, information went to ministers on Thursday evening, within minutes a decision was taken on advice on recommendation to close the bridge that evening.”

Mr Mackay added that the two reasons for closure were one, not to compromise safety, and second not further damage the structure of the bridge.

Timeline of the Forth Road Bridge closure

Tuesday 1 Dec: Failure of the inner link support beam to the north east tower truss end link was identified during an inspection at 15:30.

Closure of southbound carriageway was implemented at 21:30 with contraflow on northbound carriageway.

Wednesday 2 Dec: Specialist engineers commence structural inspection and assessment, which progressed into the night.

Thursday 3 Dec: Further assessment was undertaken with respect to alternative traffic loading and live loading on the bridge. Non-destructive testing was undertaken at the affected location and design solution was developed for both interim and permanent repairs. The structural assessment indicated significant overstress at this and other locations. Therefore the bridge was required to close for heavy goods vehicles at 14:30.

Further testing identified a likely crack in the remaining outer link support beam. After further analysis the decision was made to close the Forth Road Bridge to all traffic at midnight. Given the programme and time scales expected the bridge shall remain closed until after the New Year.