ENGINEERS have confirmed that they are on track to have the Forth Road Bridge reopened by January 4, as Transport minister Derek Mackay accused political opponents of "twisting facts" over the crisis.

Trunk road maintenance firm, Amey, said it aims to complete work to repair a crack under the carriageway in time for commuters returning to work after the festive holidays.

However, they stressed that the timetable would depend on the weather.

The Met Office currently has no weather warnings in place for the Edinburgh and Fife regions, but heavy rain is forecast for Saturday.

Chartered engineer Mark Arndt, Amey's account director responsible for the bridge, said: "Our engineers are working around the clock to get the bridge reopened to that timetable.

"It's weather dependent, however."

All traffic has been diverted along other routes since December 4 after the fault, less than an inch long, was discovered during a routine inspection.

Derek Mackay announced last week that a diversion route on the A985 between Cairneyhill and Kincardine would now be open to light goods vehicles such as vans, and to all vehicles at weekends.

They had previously been diverted along other routes towards the Clackmannanshire Bridge, freeing up the Kincardine Bridge for heavy goods vehicles and buses.

The vehicle restrictions are to be completely lifted on December 23 to coincide with the start of the holiday period.

Meanwhile, Mr Mackay yesterday accused rival parties of "deliberately misinterpreting and twisting the facts for their own petty party political gain" after Scottish Labour leaked an email from chief engineer Barry Colford, dated February 24 this year, warning that vehicles weighing more than 150 tonnes would have to be banned from the bridge until its truss end links were either strengthened or replaced.

The crack which has closed the Forth Road Bridge is located on one of the truss end links, but Transport Scotland has stressed that the fault developed recently and was unrelated to Mr Colford's email.

In a separate development, it emerged that the 51-year-old bridge's expansion joints were described as a "safety and maintenance liability" eight years ago in a report to the now defunct Forth Estuary Transport Authority.

The main expansion joints are essential for allowing the deck of the Forth Road Bridge to expand and contract as required by weather or weight of traffic.

However, works to replace the joints were put off until 2016 after costs soared and the Scottish Government announced that the new Queensferry Crossing would be in place the same year.

A spokesman for Transport Scotland said the "bottom line" was that FETA had taken the decision over the repairs programme, not ministers, adding that public spending watchdog Audit Scotland has never referenced "critical maintenance being neglected as a consequence of underfunding".

Questions over the bridge's maintenance record have led to calls for a public inquiry, however, amid complaints that its closure is threatening the livelihood of some small businesses who rely on the Fife-Edinburgh route.

Mr Mackay said his priority was to reopen the bridge, which carries an average of 70,000 vehicles per day.

He also thanked travellers for their "patience and forbearance" as Transport Scotland reported that peak journey times on the A907 diversion route are now down by 30 minutes as the public have adapted to the bridge closure.

Stagecoach is reporting typical journey times of one hour 30 minutes on its Fife-Edinburgh coach services, laid on for the duration of the closure, while ScotRail has added 10,000 extra seats per day to services crossing the Forth Rail Bridge.