Senior Security Engineer - Contract

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

Job summary

Flagstone is hiring a senior security engineer to own and operate detection and response across Azure cloud security tooling. You will tune Microsoft Sentinel, coordinate with engineering squads on vulnerability remediation, and drive security posture improvements in Defender for Cloud.

The role emphasises IaC work with Terraform/Bicep and incident-response coordination. The successful candidate will have strong SIEM experience, Azure security skills, and a fintech background.

Qualifications

• Hands-on SIEM experience and cloud security expertise across Azure.
• Experience coordinating vulnerability remediation with engineering teams.
• Familiarity with AI security considerations and securing AI workloads.
• Ability to perform threat modelling and articulate security risk to stakeholders.
• Proven track record in a fintech/financial services environment is a plus.

Responsibilities

• Own and operate alerting and monitoring, ensuring stable detection and response across transitioning systems.
• Maintain and tune Microsoft Sentinel deployment, manage data connectors, reduce alert fatigue.
• Operate Defender XDR and Defender for Cloud, including policy management and posture improvement.
• Maintain automated security checks in delivery pipelines (shift-left).
• Coordinate penetration test engagements and remediation with engineering squads.
• Support data-loss-prevention controls and safeguards around AI workloads and data exposure.
• Triage and investigate suspicious activity surfaced by Sentinel/Defender and coordinate incident response.
• Contribute to detection-as-code and infrastructure-as-code (Terraform/Bicep).

Skills

SIEM experience

Azure security

Terraform / Bicep

Vulnerability remediation

AI security considerations

Threat modelling

KQL proficiency

Fintech experience

Education

SC-200 (Microsoft Security Operations Analyst)

Tools

Microsoft Sentinel

Defender for Cloud

Entra ID

Terraform

Bicep

Job description

What is Flagstone?

Flagstone is many things. An online savings platform, reinventing how individuals, businesses, and charities manage, protect, and grow their cash. A diverse group of people, bound by a collaborative spirit, and shared purpose. And lastly, a thriving, profitable business – where smart people do their best work.

Each definition shares a common thread: our unique culture. It’s our pride and joy. And our competitive advantage.

A feel for our culture:

To revolutionise the savings market, we need to be at our best. But high performance takes more than talent – it takes a culture of kindness, respect, and growth. That’s why we’re building a diverse, inclusive community, where your voice is heard and valued. Where, with close support and room to develop, you can surpass even your own expectations. And be rewarded for it. We may not change the world, but wecan change the world of financial technology. And all it takes is a winning mix of drive, talent, and empathy. Our culture celebrates all three.

But enough about us. Let’s talk about you.

About the team

Security Engineering is a team of five covering cloud security, detection, and security operations. They work directly in the Azure estate and are close to the infrastructure, not abstracted behind a policy layer. The team runs Microsoft Sentinel, Defender XDR, and Defender for Cloud, and manages tooling through infrastructure-as-code. They run a quarterly penetration test programme and are continuously building out our detection and response capability. It's a small team with broad scope, which means your work is visible, your opinions are heard, and there are meaningful problems for our engineers to work on.

This is a contract role, so we're looking for someone who can hit the ground running. You'll bring immediate impact and add value from day one, working independently without a long ramp-up. Your work will be visible, and the problems you solve will matter.

Does this sound like you?

You're a senior security engineer who operates credibly across cloud security, detection tooling, and incident response, without being narrowly specialised. You own meaningful parts of the security stack, contribute hands-on to Azure cloud hardening, and show up reliably when incidents need investigating or pen test cycles need coordinating. You're energised by visible impact, your work matters, and your voice is heard.

What you’ll do:

• Own and operate our alerting and monitoring capability through a transition period, keeping detection and response steady.
• 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.
• Maintain and extend automated security checks in our delivery pipelines (shift-left).
• Drive down time-to-fix on known vulnerabilities, coordinating remediation with engineering squads.
• Support data-loss-prevention controls that reduce the risk of sensitive data leaving the business.
• Support safeguards around how the business accesses and uses AI, including securing AI workloads and their data exposure.
• Investigate suspicious activity surfaced through Sentinel and Defender: triage, elevate, or contain as appropriate.
• Support incident response, including containment, evidence gathering, and post-incident review.
• Contribute to detection-as-code and infrastructure-as-code (Terraform or Bicep) for security tooling.
• Coordinate penetration test engagements (scope, logistics, findings review) and work with engineering teams to prioritise remediation.

What you’ll bring:

• 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.
• Experience driving vulnerability remediation cycles with engineering squads.
• Familiarity with data-loss-prevention controls.
• Familiarity with AI security considerations (securing AI workloads, data exposure risks) and/or using AI tooling to augment security engineering workflows.
• Ability to contribute to threat modelling and communicate security risk clearly to engineering and product audiences.
• A growth mindset and genuine curiosity to keep learning.
• SC-200 (Microsoft Security Operations Analyst) certification.
• KQL proficiency for detection rule authoring and threat hunting.
• Experience working in a similar fintech or financial services environment

All are welcome:

At Flagstone, we’re assembling a diverse team that defies our industry’s norms. Think this role could suit you? no matter your background.