The Modernisation Paradox: Why your oldest systems may be your greatest assets

People talk about “legacy” systems like they’re barriers to progress that need to be scrapped and replaced with new tech. But the truth is more nuanced. Yes, legacy systems have real risks and cost implications, but they also offer significant value. When deciding on the best course of action for addressing legacy systems, you need to consider both factors.

Let’s be honest: old systems do bring some real and significant problems. As they get older, they’re more likely to have security issues, especially if they’re no longer supported by the company that made them. It’s also harder to find people who know how to keep them running, which means organisations are at risk if those people leave.

And, of course, the cost to maintain them keeps growing as you patch things together year after year. This is a big deal for the public sector, where budgets are tight and services can’t just stop because something breaks. Older systems can also make it hard to adopt AI because they weren’t built to share data, connect easily with other tools, or support the technology that modern AI needs to work well. 

The value you can't see: Legacy as institutional memory

But that doesn’t mean we should ignore the good these systems do. Legacy systems, or maybe a more accurate label - heritage systems - are the result of years, sometimes decades of investment and learning. They’re packed with business logic and processes that have been proven to work in the real world.  Along with technical debt, they also bring intellectual capital - an institutional memory that extends beyond data.

Legacy systems embody organisational learning; they've been shaped by real-world usage, adapted to specific user needs, and refined through operational experience. They represent a form of collective intelligence that's incredibly difficult to replicate.  In short, they hold a lot of the organisation’s know-how, and it’s not easy to just replace that overnight.  

Modernisation: It's all or nothing

So, when it’s time to modernise, digital and IT leaders shouldn’t just look at what’s old or new. They need to weigh the risks of keeping these systems, like cost, security, and key man risk, against the value those systems still bring. That means looking at more than just the age of the technology: it’s about understanding how these systems help keep things running smoothly and how much knowledge is built into them.

Sometimes, it’s better to improve what you already have, or to mix old and new, instead of throwing everything out and starting again.  It’s also significantly less risky. 

Over my time at PDMS, the most successful modernisation approaches have been based on recognising the risks, but not forgetting the value. Rather than advocating for a complete rip and replace, we’ve found that often  the best answer is to update the old systems over time, connect them to new tech via APIs, or keep the bits that work well. 

Modern best practice is to build integration layers that connect your existing systems with new technologies. This lets you keep things running smoothly while gradually adding new features and improvements. What matters most is finding the right balance, so that the organisation can keep providing reliable services and be ready for the future, too.

Don't forget the human factor: Change management is key

One undeniable fact that we’ve learnt over the years is that successful heritage system modernisation needs to be backed up by change management strategies that recognise both the institutional and emotional investment that staff have made in established systems that they’ve used daily for years. It’s very easy to overlook the emotional dimension of transformation. 

The most effective leaders I've observed create space for this attachment while building excitement for enhanced capabilities. They frame modernisation as evolution rather than replacement, emphasising how new capabilities will amplify rather than replace existing strengths and encourage high levels of stakeholder engagement from the get-go.  

Smart, sustainable paths to modernisation 

When considering how to modernise heritage systems, it’s essential to focus on approaches that blend pragmatism with respect for institutional knowledge. Here are some practical guidelines for public sector leaders and teams based on PDMS’ tried and tested approach: 

• Start with a thorough assessment: Map out not just the technical components of your legacy systems, but also the business processes and rules they support. Engage with end users and system maintainers to capture the undocumented practices and workarounds that keep things running.
• Prioritise incremental change: Rather than aiming for a “big bang” replacement, use PDMS principles to identify high-impact, low-risk areas for improvement. Pilot small integrations or upgrades that demonstrate value and reduce disruption.
• Document institutional knowledge: Treat legacy systems as living repositories of operational wisdom. Allocate time and resources to extract, document and, where possible, automate key business rules and decision flows before any changes are made.
• Adopt interoperability standards: Focus on designing interfaces and APIs that allow legacy platforms to exchange data with modern applications. This enables a gradual transition, supports data consistency, and preserves business continuity.

To support this approach, we’ve just launched a Digital Foundations Framework tailored for the public sector.  Built on extensive experience, it’s designed to work within government realities - budget cycles, procurement constraints, and the need for gradual, risk-managed change. Each step empowers your team to modernise at your own pace, staying in control and adapting to change to meet your timelines and operational realities.

Ultimately, your heritage systems aren't holding you back; they're the very platforms upon which thoughtful, sustainable modernisation can be built. The key is learning to see them not as problems to be solved, but as assets to be developed with care and strategic intent. Liberate your legacy!  

Visit our Digital Foundations Framework page to learn more about how we can support your legacy system modernisation