The UK-based practice has been asked to compete against up to four other practices to carry out the expansion of the sacred site in Saudi Arabia, despite employees from the UK firm being incapable of visiting the city unless they are Muslim.
The details of the competition are unclear, and even Barton Willmore is not certain how many practices it is up against.
The practice was invited to submit plans following its involvement in various projects in the Saudi capital Riyadh, where it is currently working on a bird sanctuary and wetlands, as well as competing for the King Abdullah International Gardens scheme against the likes of HOK.
It is understood that the Mecca plans follow an ongoing development to expand the area around the central Kaaba mosque as it struggles to accommodate the increasing numbers of worshippers visiting on their annual Hajjpilgrimage.
Last year more than 300 of the estimated 2 million worshippers were crushed to death during the annual ritual, and a further 300 were taken to hospital due to their injuries.
According to various sources, the expansion project includes more than 60,000m 2of extra prayer space, in addition to a further 86,000m 2of space in the surrounding plaza.