THE Conservative Party have referred themselves to the data protection watchdog following an alleged breach after they revealed hundreds of email addresses in a pitch to sign up for their annual conference.

The party’s registration team, urging supporters to complete their applications for conference, reportedly copied in more than 300 addresses in a way that meant they could be seen by all recipients.

The Information Commissioner’s Office (ICO), which enforces data protection, suggested the party had failed to use blind carbon copy (BCC) - sending an email to multiple people and wanting to keep addresses private – correctly.

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It said: “The Conservative Party have made us aware of this incident and we are assessing the information provided.

“Failure to use BCC correctly in emails is one of the top data breaches reported to us every year.

“Organisations should consider using alternatives to BCC such as bulk email services, mail merge, or secure data transfer services, so personal information is not shared with people by mistake.”

The blunder came on the same day that Rishi Sunak shifted his electoral pitch to the country to focus on national security as he mentioned Scottish nationalists in a speech on extremism.

A Tory party spokesperson told The Telegraph: “We are aware of an issue relating to a conference registration email and are currently investigating the cause of this.

“We apologise to those affected and have self-reported to the Information Commissioner’s Office.”

Elsewhere, a Labour Party source told The Guardian: “On the day Rishi Sunak proclaims the Tories as the great protectors of our national security, it turns out they can’t even protect a database of contacts. You couldn’t make it up.

“The country can’t risk another five years of the Conservatives, who have hollowed out our armed forces and turned Britain’s borders into a sieve.”