Insurance company Zurich lost the personal data of 51,000 UK customers during a routine transfer to a data storage centre in South Africa in August last year.

In some cases - depending on the type of policy held by the customer - the lost data includes personal contact information including addresses and telephone numbers.

The firm said there was no evidence the data had been misused, but that the tape's location was still unknown.

The company has written to all those affected outlining what precautions they can take to avoid potential frauds.

Zurich has brought in accountancy firm KPMG to conduct an investigation, it has stepped up security surrounding the transportation of tapes, and informed the UK Information Commissioner of the loss.

"We apologise to any customers affected by this unfortunate matter. We take the security of our customers' data very seriously. What has happened is unacceptable to us," said Annette Court, chief executive of general insurance in Europe for Zurich.

"We are putting a great deal of investment into strengthening our internal processes to ensure that incidents of this nature do not happen again."

Zurich is offering to pick up the cost of any ID protection cover affected customers might need to take out.

It has set up a UK helpline - 08000 152 183 - for any policyholders who may have concerns. Customers outside the UK can dial +44 1709 764 401.