Europe has seen a rapid increase in the frequency and intensity of hot extremes in recent decades. In this study it is shown, using ERA5 reanalysis data 1960-2021, that the hottest summer days in North-West Europe are warming faster than the mean summer day. The magnitude of the difference in maximum and mean temperature trends cannot be explained by natural variability alone. Worryingly, this trend difference is not captured by comprehensive climate models. The dynamics of conditions leading up to the hottest days are investigated using lagged composite analysis. It is suggested that the difference in maximum and mean trends can be explained by a differential rate of warming between subtropical and mid-latitudes. That is, hot extremes over North-West Europe are often driven by advection of warm air from further south. Subtropical latitudes are warming faster than the mid-latitudes, hence the difference in temperature between ambient mid-latitude air and air advected from lower latitudes, is increasing. These findings suggest that North-West Europe will continue to experience ever more extreme summer temperatures and the findings provide motivation for further research into understanding differences between North Atlantic temperature / circulation trends in models and observations.