The assimilation of carbon by terrestrial vegetation via photosynthesis, or gross primary productivity (GPP), is a vital part of the carbon cycle. This process may be hampered locally by drought stress on vegetation. In a warming climate with droughts occurring more frequently, quantifying the associated deficit in carbon uptake, as attempted in this study, becomes crucial for refined regional greenhouse gas budgets. These are needed, for example, in assessing CO2 mitigation strategies involving forestation or avoidance of land-use change. In summer 2018, a drought paired with temperatures above average prevailed on the British Iles and most other parts of transalpine Europe. Using satellite images of solar-induced chlorophyll fluorescence (SIF) from the Global Ozone Monitoring Experiment-2 (GOME-2) and GOSIF data, which is based on satellite images from the Orbiting Carbon Observatory 2 (OCO-2), a GPP deficit of −98 ± 19 gC m−2 between June and September 2018 and −139 ± 25 gC m−2 for the whole year 2018 was retrieved for the British Iles. The latter corresponds to ~44 TgC, or 44% of the mass of carbon released by anthropogenic CO2 emissions 2018 in the United Kingdom.