The full reopening of the Forth Road Bridge has been delayed by a month as repairs to a structural fault continue.

The crossing was closed to all traffic for more than a fortnight after the crack was found in December and it has remained closed to HGVs since.

Transport Scotland revealed on Thursday that the bridge was not likely to fully reopen until mid-March - a month later than originally expected.

Engineers who have been monitoring the route say that poor weather conditions limited the “sensitive” phase of the works, which need to be completed before the bridge is fully open to HGVs.

Problems with the truss end link pins in the south towers were found during load testing.

From Thursday night, however, a phased HGV trial will begin on the northbound lanes between 11pm and 4am.

Transport minister Derek Mackay MSP said: “Ninety per cent of traffic returned to the Forth Road Bridge in December and while we recognise that around 600 HGVs crossing the bridge each night does not get us to 100%, it’s a step in the right direction - with full re-opening expected in mid-March.”

He added: “We will not take any decision which could risk damaging the bridge or compromising safety, so we have taken the decision to push back the reopening of the bridge to HGVs to allow time for phase two of the repair work to be complete , with additional time added as contingency due to the effects of the weather.”

Chartered engineer and Amey’s account director for the Forth Road Bridge, Mark Arndt, said: “During the recent storms, the bridge has been closed to traffic, at times, because wind speeds have been so high and it wouldn’t be safe to have people out working in those conditions.

"Our teams are working flat out to complete the work necessary to fully reopen the bridge but our timetable is highly dependent on the weather and our priority has to be on safety.”

The Road Haulage Association (RHA) said it was "disappointed" by the news, and called on the Scottish Government to consider giving compensation to hauliers.

Their call was backed by Scottish Liberal Democrat leader Willie Rennie MSP, who described the hold-up as a "bitter blow".

RHA chief executive Richard Burnett estimated that since the bridge was closed to all traffic on December 4, the cost to the haulage industry amounts to over £37m.

He said: "For the majority of hauliers, each additional cost incurred has to absorbed. Operating margins are already tight and every penny counts. Fuel already represents a third of a haulier’s costs. An extra, unplanned, fuel bill of £30 per round trip as a result of diversions, together with a higher wage bill as a result of extended journey times will inevitably mean disaster for many of the smaller hauliers that rely on the quick access the bridge provides."

Mr Rennie said: "This news will come as a bitter blow to businesses which are already struggling as a result of the closure of the bridge, and to the communities in Fife who have experienced huge disruption as a result of the spike in heavy goods vehicles forced to find alternative routes.

"No one doubts that the engineers are doing their utmost to get things back on track but we need to see a response from SNP Ministers and support for businesses that have been affected by the closure.

“Ministers need to devise and publicise a compensation scheme for the businesses affected by the continued closure. They also deserve more transparency from Ministers on the decisions being made and the progress of the work being carried out. The Scottish Government were happy to claim credit when repair work was ahead of schedule. They must accept responsibility for this extended delay too."