This paper proposes a novel methodology to overcome the outstanding challenges in effectively assessing technology maturity to final real-world applications. The Engineering Severity Level (ESL) is a conceptual tool that provides a simple, standardised and quantitative method of assessing technology suitability to real-world environments. It is a standalone tool offering advantages in generating an evidence base for accurate technology maturity assessment and early identification of developmental roadblocks. Moreover, the tool can be applied as a universal basis to enhance TRL classification and provide further context and quantitative analysis. The benefits are exemplified in the assessment of quantum technologies for Position, Navigation and Timing (PNT) requirements in Defence applications.