This is nonsense.
They would have required a structural engineers, and possibly a highways engineers report in order to fulfill the requirements through planning and building control prior to the work taking place.
The engineers (Consultants) would have been required to provide professional indemnity insurance (As is the want of the developer) to cover any defects in their professional design / remedy of any situation.
It is unlikely, that you would have third party rights to this insurance / warranty.
DO NOT RELY ON THIS!
Your NHBC should be sufficient, and is a separate warranty, passed to you, and ensures that the conditions set by planning, and building control have been met by the delveloper during construction.
ANY DEFECT MUST BE RECOVERED THROUGH NHBC.
If you do not have NHBC or similar on offer - DO NOT BUY THIS HOUSE