The £1.35 billion bridge was originally meant to open in December 2016 but was postponed until May this year after bad weather delayed work.

Now economy secretary Keith Brown has today confirmed that it would not be ready before July, with the possibility that it could be as late as August.

Speaking at the Scottish Parliament’s rural economy and connectivity committee, Mr Brown said high winds had prevented contractors from removing cranes and working on cable stays.

The contractor has reported there have been fewer clear weather windows than expected, particularly in relation to wind. This has delayed weather dependant activities causing them to bunch together at the end of the programme to a much greater degree than was anticipated in May 2016. This means that a lot of construction activity is underway simultaneously and careful planning is required to ensure that this can be done safely, so that one activity does not impact on another.

At this stage of the project all remaining activities are vulnerable to weather conditions for example, the tower cranes can only be removed in wind speeds of less than 25 mph and when this is happening, it is not possible to safely work within a 50 metre radius of the crane itself. Other works are also effected: for example, work on cable stays is sensitive to wind, waterproofing the bridge deck is sensitive to rain and road surfacing is sensitive to both rain and low temperatures.

With so much simultaneous activity underway, there are no further opportunities to mitigate the effects of weather delays at this point of the construction programme.

Mr Brown said: “Today there are only nine weeks remaining to the end of May and the review has concluded that even with the best weather this date is not now safely achievable.

“I fully recognise the effort of the workforce in building this amazing new bridge. Over 13 million hours have gone into building the Queensferry Crossing over the past six years.

“There is no additional cost to the public purse and the Forth Road Bridge continues to carry traffic over the Forth during these final weeks of construction. While its clearly very disappointing the new bridge won’t be ready ahead of the contractual completion date, I believe it is important to take the time to make sure the bridge is built in the safest possible circumstances to the highest possible standards.”

Sally Cox, chair of the Board for the Forth Road Crossing Bridge Constructors (FCBC), added: “FCBC acknowledge that the uniqueness of this project and the onerous weather conditions it has experienced, particularly working at height crossing the Forth have created more challenges than we anticipated.

“FCBC have always been and remain ambitious about completing this challenging project at the earliest possible date and share Transport Scotland and the public’s frustration over this delay. We have assured Transport Scotland that every endeavour is and will continue to be made, to safely complete the project at the earliest opportunity.”

Mr Brown described the delay as a “huge disappointment” but added that the cost of the over-run would be paid by contractors, with no extra cost to taxpayers.

On the issue of adverse weather, he said: “It has taken 65 days to take down one of the cranes—it would normally have taken 15 days—because of the consistently high winds. As soon as the wind speed goes above 25mph, it is not possible to work on the cranes, and that has contributed to the delay.”

Mr Brown added: “However, this has been a seven-year project that is about £0.25bn below budget, and that will not change.”

Engineers building the new crossing said in January that there were no guarantees the bridge would open in May, adding that while the timetable was “realistic”, the weather was capable of disrupting plans.