Bad weather and windy conditions have hampered work by the Forth Road Crossing Bridge Constructors – who consist of Hochtief, American Bridge, Dragados and Galliford Try.

Economy Secretary Keith Brown confirmed the expected opening date will be achieved in a window between mid-July and the end of August – approximately 4 to 10 weeks later than predicted on a six year construction programme.

The contractor has reported there have been fewer clear weather windows than expected, particularly in relation to wind.

This has delayed weather dependent 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.

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.

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.

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 said: “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.”