The tourist attraction, which will give public access to the world-famous structure and explore its heritage as well as the outstanding views from 367 ft (110m) above sea level, was granted planning permission in March.

The project is intended to create an ‘enhanced’ tourist attraction, with the build of a visitor centre at the base of the bridge’s Fife Tower, a public viewing platform accessed by two glass lifts at the top of the tower, and a bridge walk experienced at the southern end of the bridge.

Firms have until August 3 to complete prequal documents. Four firms will be shortlisted to tender for the work which is due to get underway before the end of the year.