Senior Penetration Tester - CTM

Instil; Greater London; On-site; GBP 70,000 - 100,000; Full time

Benefits offered by this job

Performance bonus

Flexible working

Private healthcare

Life assurance

35 days holiday

Learning & certifications

Volunteer & community

Job summary

Instil is seeking a Senior Penetration Tester with CHECK to join our growing team in the UK. You will lead hands-on penetration testing across infrastructure, cloud, web, and mobile applications for a diverse client base, ment oring juniors and shaping our testing methodologies.

The role emphasizes identifying security weaknesses and delivering high-quality engagements, with opportunities to influence internal processes and contribute to challenging projects in a supportive environment.

Qualifications

• Must hold CHECK Team Member (CTM) status and current UK security clearance.
• Minimum 2+ years in penetration testing across infrastructure, web, and mobile contexts.
• Proven ability to perform web application and network pentesting using industry-standard methodologies.
• Solid OS knowledge: Linux, Windows, Active Directory; experience with cloud environments and cloud security reviews.
• Proficient with testing tools Burp Suite Pro, Nmap, Nessus, and Kali Linux; scripting in Python/Shell.

Responsibilities

• Deliver high-quality penetration testing engagements across diverse client base.
• Identify, remediate security weaknesses, and contribute to methodology development.
• Mentor junior testers and support team growth.

Skills

CTM status

UK security clearance

2+ years pentest

Web & network pentest

OS knowledge (Linux/Windows/AD)

Cloud security reviews

BurpSuite Pro/Nessus/Nmap/Kali

Scripting (Python/Shell)

Tools

BurpSuite Pro

Nmap

Nessus

Kali Linux

Job description

We are looking for a Senior Penetration Tester with CHECK to join our growing team. You will play a critical role in delivering high-quality penetration testing engagements across infrastructure, cloud, web, and mobile applications for a diverse range of clients, including software, fintech, manufacturing, engineering, legal, and public sector organisations.

This is a hands‑on role where your expertise will help identify and remediate security weaknesses, while contributing to the development of our methodologies and mentoring junior testers. If you’re passionate about offensive security and want to work on varied, challenging projects in a supportive environment, we’d love to hear from you.

Essential Skills

• CHECK Team Member (CTM) status
• Current UK Security Clearance
• At least 2+ years of penetration testing experience
• Strong experience with web application and network penetration testing methodologies
• In-depth knowledge of operating systems (Linux, Windows, Active Directory)
• Familiarity with cloud environments and ability to perform cloud security reviews
• Proficiency with tools such as BurpSuite Pro, Nmap, Nessus, and Kali Linux
• Knowledge of scripting languages (Python, Shell, etc.)

Nice-to-Have

• CHECK Team Lead (CTL) status (Infrastructure or Applications)
• Relevant certifications (OSCP, Cyber Scheme)
• Experience with Hack the Box or Capture the Flag simulations

Why Join Instil?

At Instil, we believe great work starts with happy, motivated people. That’s why we’ve built a benefits package that supports your wellbeing, growth, and life outside of work, because when you thrive, so do we.

• Recognition That Matters: A discretionary annual performance bonus that rewards your impact and contribution to our success.
• Flexibility Built In: Flexible working arrangements and summer hours, because life isn’t 9 to 5, and balance matters.
• Financial Security: A highly competitive pension scheme with generous employer contributions, private healthcare, and life assurance for peace of mind.
• Health & Wellbeing: Employee Assistance Programme, mental health support, cycle‑to‑work scheme, and regular social events to keep our culture vibrant.
• Time to Recharge: 35 days holiday, enhanced maternity pay, and family‑first policies so you can focus on what matters most.
• Learning Never Stops: From courses to certifications, we’ll invest in your development so you can keep growing and shaping what’s next.
• Community & Culture: Opportunities to volunteer, give back, and be part of initiatives that make Instil a truly inclusive and connected workplace.

Company Description

Instil has been delivering world‑class software engineering and technology solutions for over 20 years, trusted by global brands to solve complex challenges and drive innovation. From modernising legacy systems to building cutting‑edge applications, we help our clients navigate an ever‑changing digital landscape with confidence and agility.

We’re proud to be an award‑winning employer, reflecting how our people are at the heart of everything we do.

• Recognised as a Great Place to Work for three consecutive years, and in 2024 ranked in the Top 20 Best Workplaces in the UK for medium‑sized companies.
• Winner of Company of the Year at the Digital DNA Awards 2022, celebrating excellence in Northern Ireland’s tech sector.

Driven by a love for technology and a commitment to excellence, we bring together people who want to make a difference. We’ll support your journey, because your success is part of ours.