Historians and heritage experts, including those from the ASI, have called for carrying out a scientific investigation of a tunnel located beneath the sprawling building of the Delhi Assembly, which has again captured the imagination of the people.

The 'mystery tunnel', first reported around 2016, has sparked multiple speculation, and experts said it will be too early to draw any conclusion unless the structure is thoroughly examined from an archaeological standpoint or any documentary evidence is found.

The subterranean structure's mouth lies just below the floor of the assembly hall of the iconic building (Old Secretariat), which was constructed in 1912 by the British after the imperial capital was shifted from Calcutta to Delhi, and it is being planned to be thrown open to the public next year.

Delhi Assembly Speaker Ram Niwas Goel on Friday had said that historical significance of the tunnel is yet to be established but it is conjectured that the tunnel connects the assembly building to the Red Fort.

He also claimed that there was an "execution room" at the site where Indian revolutionaries were brought to by the British.

Many historians and heritage experts, including those who have done extensive research on the multi-layered history of Delhi, however, have expressed scepticism over the claims and suggested scientific investigation of the structure and the site.

A senior Archaeological Survey of India (ASI) official said that theories and conjectures abound in absence of investigation.    

"So, the structures beneath need to be seen archaeologically, first. And, even if there are obstructions due to metro and flyover pillars, technology is there to investigate to test the theory. Without investigation, it would not be wise to make comments," he told PTI.

Also, the Red Fort link theory seems a bit implausible as the distance ÿbetween the 17th-century Mughal monument and the British-era landmark is over six km, and with a low height, a tunnel that long would be hard to imagine as it would also be hard to navigate, the official said.