The Birmingham City Council document reveals the raised section of the Aston Expressway needs a £26m works programme to tackle concrete chloride attack problems.

It warns that Birmingham could suffer like London when the A4 Hammersmith flyover had to be closed for a long period to carryout emergency structural repairs.

For several years it has been known the viaduct was suffering chloride attack. But the report obtained by the Birmingham Post warns that more dramatic remedial action is now needed.

The report states: “Without action to maintain the viaduct, the risk of weight restrictions and collapse of the viaduct is considerable.

“Action is deemed necessary to maintain the viaduct and remove any risk of structural failure or of having to impose weight restrictions on the viaduct, the economic cost of which would be significant.

“A series of ever-more refined assessments have established beyond doubt that there are deficiencies within the structure.

“Thin walled box girder bridges are known to be a vulnerable form of construction and this has necessitated the strengthening of many similar major structures.”

The report adds: “A worst case scenario is total failure of the structure, similar to that of the Hammersmith Flyover in London and the M4 structure affecting the main route from Heathrow Airport into central London in 2012.”