Senior Security Engineer

Flagstone is an online savings platform reinventing how individuals, businesses, and charities manage, protect, and grow their cash. It’s a thriving, profitable business where smart people do their best work. We build a diverse, inclusive community with kindness, respect and growth. We value your voice, support development, and reward visible impact.

About the Team: Security Engineering is a team of five covering cloud security, detection, and security operations. They work directly in the Azure estate, run Microsoft Sentinel, Defender XDR, Defender for Cloud, and manage tooling via IaC. The team runs quarterly penetration tests and continuously builds detection & response capabilities.

Does this sound like you? You are a Senior Security Engineer who operates across cloud security, detection tooling, and incident response. You own meaningful parts of the security stack and contribute to Azure hardening. You show up reliably for incidents and pen test cycles. You thrive on visible impact.

What you’ll do:

• Maintain and improve our Microsoft Sentinel deployment - writing and tuning detection rules, managing data connectors, and reducing alert noise.
• Operate and optimise Defender XDR and Defender for Cloud, including policy management and posture recommendations.
• Harden our Azure environment across identity, access management, networking, storage, WAF configuration, and logging pipelines.
• Contribute to infrastructure-as-code (Terraform or Bicep) for security tooling deployments and configuration drift management.
• Investigate suspicious activity surfaced through Sentinel and Defender - triage, elevate or contain as appropriate.
• Support incident response activities including containment, evidence gathering, and post-incident review.
• Participate in security risk assessments and threat modeling exercises across new and existing systems.
• Coordinate penetration test engagements (scope, logistics, findings review) and work with engineering teams to prioritise remediation.

What we’re looking for:

• Hands‑on SIEM experience, ideally Microsoft Sentinel; equivalent platforms considered.
• Practical Azure security experience across Defender for Cloud, Entra ID, Azure networking, and cloud security posture management.
• Experience writing infrastructure-as-code using Terraform or Bicep in a security engineering context.
• Ability to contribute to threat modeling and communicate security risk clearly to engineering and product audiences.
• Experience supporting or coordinating penetration testing programmes, including managing remediation cycles.
• Familiarity with AI security considerations (securing AI workloads, data exposure risks) and/or using AI tooling to augment security engineering workflows.
• A growth mindset and genuine curiosity to keep learning.

Nice to Have:

• SC-200 certification.
• KQL proficiency for detection rule authoring and threat hunting.
• Experience in a fintech/financial services environment.

How we reward you:

• Competitive bonus scheme.
• Flexible benefits budget covering diverse benefits.
• Salary sacrifice options for electric cars, nursery schemes, home and tech goods.
• Around the World scheme – 3 months work from anywhere.
• Mental wellbeing support – therapy and mental health sessions through Spill.
• Learning and development – £1,000 personal development budget.
• Private health care – AXA benefits.
• Medical cash plan for dental and optical expenses.
• Life insurance and income protection – four times your annual salary.
• Matched pension contributions up to 5%.
• 25 days holiday plus bank holidays, well‑being days and volunteering days.
• Enhanced parental leave – maternity, paternity and adoption pay.

All are welcome. We welcome people of all backgrounds to apply.