BT (BT shares have sunk to a three-year low after the company cautioned that write-downs in its Italian business will be much larger than expected. After the news broke, shares in the telecommunications firm fell as much as 18.75%, the biggest single-day decline in eight years. 

The announcement of a write-down of £530 million, well above the originally estimated £145 million, comes after an internal audit into BT's Italian unit.

Commenting on the Italy probe, CEO Gavin Patterson said, "We have undertaken extensive investigations into that business and are committed to ensuring the highest standards across the whole of BT for the benefit of our customers, shareholders, employees and all other stakeholders."