Senior Cloud Security Engineer - Azure & SIEM

Flagstone; Greater London; Hybrid; GBP 90,000 - 120,000; Full time

Benefits offered by this job

Competitive bonus scheme

Flexible benefits budget

Salary sacrifice options

Around the World scheme - 3 months

Mental wellbeing support

Learning and development budget

Private health care

Medical cash plan

Life insurance and Income Protection

Matched pension contributions up to 5%

25 days holiday + bank holidays

Enhanced Parental Leave

Job summary

Flagstone is building a cutting-edge online savings platform in the UK, combining risk-aware security with a flexible, hybrid work culture. We seek a Senior Security Engineer to own substantial parts of our security stack, contribute to Azure hardening, and drive incident response and threat modelling across our cloud environment.

You’ll work on Microsoft Sentinel, Defender XDR, and Defender for Cloud, leveraging Terraform or Bicep for security tooling deployments.

Qualifications

• Hands-on SIEM experience, ideally Microsoft Sentinel; equivalent platforms (Splunk, Chronicle, QRadar) 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 modelling 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

Responsibilities

• Maintain and tune 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 modelling exercises across new and existing systems
• Coordinate penetration test engagements (scope, logistics, findings review) and work with engineering teams to prioritise remediation

Skills

Microsoft Sentinel

Defender for Cloud

Azure security

Terraform

Bicep

Threat modelling

Pen testing coordination

AI security

Tools

Terraform

Bicep

Job description

Flagstone is building a cutting-edge online savings platform in the UK, combining risk-aware security with a flexible, hybrid work culture. We seek a Senior Security Engineer to own substantial parts of our security stack, contribute to Azure hardening, and drive incident response and threat modelling across our cloud environment.

You’ll work on Microsoft Sentinel, Defender XDR, and Defender for Cloud, leveraging Terraform or Bicep for security tooling deployments.