The UK public sector spends more than £26 billion a year on digital technology and employs almost 100,000 digital and data professionals, yet legacy systems, fragmented data, funding constraints and skills gaps continue to slow progress.  

As artificial intelligence increases pressure on departments to automate, personalise and improve services, outdated estates can quickly become a blocker rather than a foundation for reform. 

Fewer organisations are set out to run critical services on ageing technology. Legacy systems accumulate quietly. A platform that still works is rarely the loudest priority, and the cost of replacing it always seems easier to defer for another year.  

But deferral is not free.  

In the UK, legacy technology failures are now estimated to cost the public purse around £45 billion a year, with lost productivity alone running at 4-7% of total public sector spending. Roughly 28% of central government systems are still classed as legacy, and the figure is far higher in parts of health and policing.

That message was reinforced at DigiGov Expo on 23 September 2026, when Alex Baird from Government Digital Service spoke on the panel, “Strategic Transformation: Navigating policy, process and cross-government delivery.” He highlighted that the UK Government has underestimated the scale of legacy systems still in use across the public sector, and that departments need to quantify risk in financial terms if they are to make stronger, evidence-based decisions about modernisation. 

At Certes IT, we have taken that challenge and turned it into a practical approach. 

Drawing on HM Treasury policy, the Green Book and its supplementary guidance, we have developed a legacy system calculator built around seven government-led indicators from the Legacy IT Risk Assessment Framework. 

The questionnaire gives departments an estimated view of what an ageing system may be costing them, not only in direct spend, but also through productivity loss, operational risk and the limitations it places on service reform. 

From there, teams have a clearer starting point for action, with practical recommendations that can range from refreshing the existing system to planning a full overhaul and replacement where the risk and cost justify it. 

Click on the link below to view our Legacy System Calculator tool, complete the questionnaire, and you’ll receive personalised results, practical recommendations and clear next steps to help elevate your technology strategy.