Top Cybersecurity companies in London

Telos Corporation (NASDAQ: TLS) empowers and protects the world’s most security-conscious organizations with efficient, adaptable, and secure solutions that safeguard people, systems, and information. We deliver advanced capabilities across cyber governance, risk, and compliance (GRC) with Xacta®; identity and biometric solutions; secure networks and communications; and TSA PreCheck® enrollment services. Serving the U.S. federal government, regulated industries, and global enterprises, Telos helps customers stay ahead of evolving threats, accelerate compliance, and achieve mission success. Driven by purpose and guided by our core values, we build trusted partnerships, deliver superior solutions, and help create a more secure, interconnected world.At Telos, we realize that our success as a company stems directly from our success as an employer. That is why we are committed to finding, attracting, and keeping the best talent available. We reward expertise with professional growth and opportunity, an excellent salary, a flexible work environment, and a robust benefits package. We recognize the challenges a demanding job can place on families, so we do our best to accommodate work-life balance. If this appeals to you, we invite you to put Telos on your career path.Headquartered in Ashburn, Virginia, outside the Washington, D.C. metropolitan area, Telos Corporation is located in the heart of the Dulles technology corridor. We’re always looking for employees who share our core values and want more than just a job. We offer a business casual environment, and the opportunity to make a name for yourself as you contribute to our continued success. If you’re interested in joining our team, visit our careers page: www.telos.com/careers.

• Series unknown
• 673 employees
• Founded 1971

In an era where data is the most valuable currency, Network Security Labs (NSL) stands as the definitive line of defense. We aren't just a service provider; we are architects of digital resilience, dedicated to outthinking threats before they become breaches.Founded by a collective of elite cybersecurity engineers and ethical hackers, NSL was born from a simple realization: static defense is no longer enough. Today’s adversaries are dynamic, automated, and relentless.

• 447 employees

In a world where cyber threats evolve daily, your business deserves protection that stays one step ahead. We're a cybersecurity agency dedicated to defending organisations of every size against the risks that matter most — from ransomware and phishing to data breaches and insider threats.Our services span the full security lifecycle: penetration testing, vulnerability assessments, 24/7 threat monitoring, incident response, cloud security, and compliance support (ISO 27001, GDPR, Cyber Essentials). Whether you need a one-off security audit or a fully managed security operation, we tailor our approach to your business, your budget, and your risk profile.What sets us apart? We speak business, not just tech. Every recommendation we make is grounded in real-world impact — protecting your revenue, your reputation, and your customers' trust.Cybersecurity isn't a product. It's a partnership.Protect what you've built. Get in touch today.

• 442 employees

CREST is an international not-for-profit, membership body representing the global cyber security industry.Our goal is to help create a secure digital world for all by quality assuring our members and delivering professional certifications to the cyber security industry.We accredit 500+ member companies, operating across dozens of countries, and certify thousands of professionals worldwide. We work with governments, regulators, academe, training partners, professional bodies and other stakeholders around the world.Our members undergo a rigorous quality assurance process and employ competent professionals. Organisations buying their cyber security services from our members do so with confidence.We have regional chapters covering the Americas, Asia, Australasia, EMEA as well as the United Kingdom which is our founding chapter.It is a devolved structure based on elected Regional Councils representing member companies operating in those regions. Central services are provided by CREST International.

• Grant
• 429 employees
• Founded 2006

Pen AI is an AI-native offensive security platform designed to close the gap between rapid development and rigorous security.In a world where 24/7 deployment is the norm, annual pentesting is no longer enough. Pen AI provides continuous, autonomous penetration testing that mimics the tactics of real-world adversaries. Our platform orchestrates hundreds of specialized security tools to map attack surfaces, chain vulnerabilities, and provide actionable evidence-based reports in minutes, not weeks.Core Capabilities:Autonomous Reconnaissance: Real-time mapping of your evolving digital perimeter.Intelligent Exploit Validation: We move beyond "red flags" to provide verified proof-of-concept.Context-Aware Reporting: Seamlessly integrates with Jira, Slack, and your CI/CD pipeline.We’re here to empower developers and security professionals to build with confidence, knowing their perimeter is constantly being tested by the smartest agent in the room.

• 362 employees