The personal details of 34,000 Boots customers and employees have been stolen from a courier car.
The stolen data tapes included names, addresses and bank details of the pharmacy's dental plan customers, which is run by private healthcare contractor Medisure.
The tapes were taken from the car of a subcontracted data security company.
Medisure said the tapes were not in a consumer format and would only be accessible with specialist IT equipment.
Boots said in a statement that the firm involved has already informed affected Dental Pan customers, as well as other appropriate bodies.
"We would emphasise that Medisure has informed the Financial Services Authority and the Information Commissioner. Medisure has also ensured that as a precaution our customer's banks have been informed so that they can monitor affected accounts for any unusual activity," the statement says.