Principal Software Engineer - (.Net, PHP, Umbraco, Drupal)

You define architecture that is appropriate to the client's budget, team and long-term maintenance capability, not to the most interesting technical solution available.

You uphold a clear software design philosophy and ensure teams deliver maintainable solutions.

You have a clear understanding of simplicity. You define solutions that are simple by design and challenge requirements that introduce unconsidered complexity.

You identify and challenge ineffective practices in delivery teams and in client organisations.

You delegate, and maintain clear separation from work that should be considered routine.

You make hosting, infrastructure and platform decisions with a clear view of cost, security and who will be responsible for what after launch.

You are the senior technical escalation point across the estate

You diagnose and resolve complex problems in codebases you did not write and may not have seen before.

You lead the technical response to significant incidents, establishing root cause and directing remediation.

You give clients and internal teams confidence at the point where things have gone wrong, through clear communication and visible control of the situation.

You identify the systemic causes behind recurring problems and drive the changes that stop them repeating.

You raise the standard of engineering across the department

You are an active and visible technical leader across the company.

You mentor lead and senior engineers, building capability rather than absorbing the hard work yourself.

You contribute to and uphold our engineering standards, technical governance and software development lifecycle.

You demonstrate your passion for keeping on top of current tools, standards and trends, including AI-assisted engineering practice.

You support marketing and new business with prototypes, thought leadership or presentations where it plays to your strengths.

You create learning within the team by specifying solutions that further our collective knowledge and give others opportunities to grow.

Cross-stack technical depth. Genuine working expertise across more than one platform and language, specifically .NET and Umbraco alongside PHP and Drupal. Comfortable holding technical authority in both rather than being deep in one and passing in the other.

Architectural leadership. Expert in designing robust, scalable and secure architectures for content-managed platforms, integrations and modern web applications.

Cloud and infrastructure. Practical, hands-on experience with cloud platforms, particularly Azure, including CI/CD pipelines, infrastructure as code and managed hosting environments. Enough depth to make infrastructure decisions and resolve infrastructure problems with minimal support.

Diagnostic ability under pressure. Proven ability to enter an unfamiliar codebase, establish what is happening quickly, and lead resolution. This is a defining requirement of the role.

Pre-sales and technical discovery. Experience qualifying opportunities, running technical discovery, producing solution designs and estimating work before it is sold.

Software engineering principles. Mastery of clean code, testing practice, design patterns, security and accessibility standards.

Leadership and mentorship. Demonstrated experience developing lead and senior engineers, raising standards through others rather than personally absorbing the difficult work.

Commercial awareness. Understands that technical decisions carry margin, risk and maintenance consequences, and factors this into the solutions proposed.

Communication . Outstanding ability to explain complex technical concepts to non-technical stakeholders, and to hold client confidence when things are difficult.

Strong hands-on experience with content management platforms across more than one stack, specifically Umbraco and .NET, and Drupal and PHP

Practical cloud engineering experience, primarily Azure, including CI/CD pipelines, infrastructure as code and environment management

Experience across managed hosting platforms such as Azure, Acquia, Umbraco Cloud, WP Engine or Pantheon

API design and integration, REST and GraphQL, including third-party systems such as CRM, payment and marketing platforms

Security by design and DevSecOps practice, with particular awareness of handling supporter and donor data

Accessibility standards and practice, WCAG 2.2 and above

Version control, branching strategy and release management at scale across multiple codebases

Agile delivery practice, and how to make it work in a client services context

Headless and decoupled CMS architecture

Authentication and identity, including OAuth and SSO

Search implementation, including AI-assisted and hybrid search

AI-assisted engineering practice, agentic tooling or AI-enabled development workflows

Experience of the charity, non-profit or membership sector and its particular constraints

You are the person others want on the call when something has gone wrong. You stay calm, establish facts quickly and communicate clearly under pressure.

You are pragmatic rather than purist. You choose the simplest approach that meets the need and challenge complexity that is not earning its place.

You proactively define and champion the long-term technical direction, ensuring it aligns with business goals and client reality.

You actively develop and empower other engineers, sharing knowledge and building capability rather than becoming a single point of dependency.

You move comfortably between client contexts, quickly getting up to speed while maintaining the focus needed to provide effective technical leadership.

You engage confidently with stakeholders across the business and in client organisations, translating technical concepts and influencing decisions.

You resolve conflicting requirements and differing opinions into a plan all parties can support.

You set high standards for quality, reliability, security and maintainability, and hold others to them constructively.

You seek out new technologies and approaches that deliver genuine value, and are honest about the ones that do not.

You embody Manifesto's values, championing purpose-driven work and fostering a positive team culture.

We are the digital experience agency for changemakers. We are committed to delivering purposeful and positive impact for people, planet and society, in restless pursuit of a better world.

We take pride in creating award-winning digital experiences, products and services that are measurably ethical, inclusive, accessible, sustainable and joyful.

Our changemaker clients include UNICEF UK, Breast Cancer Now, Trussell, Woodgreen, The Royal Academy of Arts, Zoological Society London, Historic Environment Scotland and Fauna & Flora.

Part of the TPXimpact group - a Certified B Corporation™, we are a team of 130 digital product leaders, creative designers, user experience designers, engagement specialists, software engineers and experience strategists.

TPXimpact is a digital transformation company, and Certified B Corporation™, on a mission to build a future where people, places and the planet are supported to thrive. Combining vast expertise in human-centred design, data, experience and technology, we help the public, private and third sectors with their digital transformation journey, delivering high quality solutions that improve services, experiences and outcomes. We’re passionate people who work in close collaboration with our clients to create sustainable solutions ready for an ever-evolving world.

We are committed to having a positive impact on the clients and the communities we serve. We actively encourage applications from all genders, ethnicities, disabled people, members of the LGBTQIA+ community, and those from lower socio-economic backgrounds.

Don’t meet 100% of the criteria? We still want to hear from you. Please let us know if you require any adjustments during the recruitment process.

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