The new hospital will provide over 800 beds and will remain London's busiest major trauma centre.
St Mary's Hospital estate is one of the oldest in the NHS with parts dating back to 1845.
The hospital has the largest maintenance backlog, which has increased by 22.5% (£157m) in the last four years, £53m above what the trust has been able to spend on addressing issues.
Imperial College intends to the close of its main outpatient building by 31 March following the discovery of reinforced autoclaved aerated concrete.
In addition, immediate stabilisation works are being carried out at its Mint building following the discovery of significant foundation issues.
The trust is exploring additional financing sources and models to begin the main building works for St Mary's by 2035 ahead of the current New Hospital Programme which delays delivery to 2043 at the earliest.
Imperial College plans to complete the design work and submit a planning application – for the new hospital and the wider masterplan – by spring 2027.
