A box of premium customers' bank details, including those of three lottery winners, was found near a road connected to the British highway.
The files in the box related to multi-million-dollar investments and included in the package were cheques and other sensitive papers which could have been used by fraudsters if they had fallen into the wrong hands.
Luckily, a vehicle recovery driver found the box on a roundabout near Junction 11 of the M4 highway near Reading in Berkshire.
It was ascertained that the box had fallen out of a courier van supposed to be transporting the files from a Prudential branch in Reading to a secure storage facility in Essex.
A spokesman for Prudential said: "Protection of our customers' data is of paramount importance to us and we are contacting them immediately. The key thing is that none of those customers will suffer any financial loss as a result of this."
Prudential itself could have suffered massive losses as a result of the blunder, as it would have been obliged to cover its customers under the Banking Code.