Why Third-Party Data Breaches Are a Growing Threat in UK Businesses — And What You Can Do About It

• by Olivia Lawlor-Blackburn
• Advent IM Blog

October is Cybersecurity Awareness Month — a great time to think about not just your own systems, but the security of all the parties you depend on. Recent incidents show that third-party breaches are more than theoretical risks — they’re happening now, and hitting UK organisations hard.

What’s going on now

Here are some real examples and statistics to illustrate the scale and kinds of risks:

• Over half (51%) of UK organisations reported experiencing a breach or cyber-attack in the past 12 months that involved a third party accessing their network. GlobeNewswire
• Renault UK disclosed that personal and vehicle data of its customers was stolen in a cyber-attack against one of its data processing providers. Financial info was not compromised. Cybersecurity Dive
• Heathrow (and other major airports) faced major disruptions when a third‐party check-in software provider (Muze via Collins Aerospace) was hit by ransomware. Flights were delayed, airline operations disrupted. Zensec
• The legal sector saw breaches up 39% year-over-year in Q3 2023-Q2 2024, affecting ~7.9 million people in the UK. A large portion of those involve external threats (phishing, etc.) that often leverage third-party relationships. PR Newswire

Why third parties introduce so much risk

Here are some of the main reasons these breaches are happening:

• Wider attack surface: Every vendor, supplier, outsourced service provider, cloud partner becomes another potential entry point. If their security is weak, it puts you at risk.
• Lack of visibility or control: Organisations often don’t have full insight into how third parties store, protect, or use data.
• Poor vendor risk management: Sometimes oversight is minimal: contracts don’t demand strong security, audits are infrequent, or monitoring is weak.
• Remote access & privileged access misuse: Third parties are often given broad or privileged access (e.g. access to internal systems) which, if compromised, can do a lot of damage.
• Supply chain dependency / resilience issues: When a third party fails, the impact can cascade — downtime, service disruption, customer trust loss.

What UK businesses can do now

To protect yourselves, here are best practices and actionable steps:

Key takeaways

• Having strong internal security isn’t enough — your security is only as strong as your most vulnerable external partner.
• Even if you don’t suffer direct data loss, third-party breaches can damage trust, lead to regulatory and financial penalties, hurt operations, and tarnish reputation.
• Proactive risk management is cheaper, faster, and less painful than reacting after things go wrong.