A statement on the company’s website says: ‘We believe there has been some unauthorised access using an internal login to the data of a small number of our UK customers so we are working closely with the authorities to investigate the situation.

‘Our customers are always our first priority so we are communicating directly with those who may be affected and giving guidance on measures they can take to protect their security.

Anyone who has any concerns is advised to call a dedicated helpline number, which is 0845 145 3345. They should leave a message with their details, or alternatively email [email protected].

The company has not confirmed when the breach occurred, although it is thought to have happened within the last few weeks, with around 280 businesses affected according to a BBC report. Nor is it clear whether the information was stolen, or simply viewed without permission.

Sage has reported the incident to the City of London police and the Information Commissioner’s Office (ICO), which enforces the Data Protection Act, has been informed.

If the ICO decides that Sage has been negligent there are a number of actions it could take, including criminal prosecution, non-criminal enforcement, or undertaking an audit at the firm.

In a statement, Sage said: ‘We cannot comment further whilst we work with the authorities to investigate - but our customers remain our first priority and we are speaking directly with those affected.’