The results of 61 in situ UK thermal response tests, derived from three commercial test-rigs, have been analysed. Derived values of thermal conductivity yield a median of 2.25 W m K−1, with 25th and 75th percentiles of 1.86 and 3.0 W m K−1. The lowest single values are derived from Northern Irish basalt (1.1 W m K-1) and from Mesozoic and Tertiary argillites (often in the range 1.43–2 W m K−1), whereas the highest (>5 W m K−1) are from Sherwood Sandstone and Coal Measures strata where advective heat transport with groundwater flow may have led to an elevated apparent conductivity. Borehole thermal resistance exhibits 25th percentile, median and 75th percentile values of 0.09, 0.11 and 0.14 K m W−1 and correlates with borehole heat exchanger diameter and configuration. Undisturbed ground temperature exhibits 25th percentile, median and 75th percentile values of 11.7, 12.3 and 13.2 °C and exhibits a latitude dependence.