An extensive intercomparison has been made between the daily averaged reduction factors in UV irradiance due to the presence of clouds as derived from ground-based (pyranometer) and satellite based measurements for the summer months of six years over Europe. Two independent satellite datasets were used for this purpose (ISCCP D1 and TOMS) and the resulting correlations between daily, 10-day and monthly averaged values are presented. In general, the correlation between the daily averaged TOMS and ground-based values matches those for the corresponding ISCCP comparisons (with typical R2 values of 0.85 and 0.8, respectively). Moreover, the monthly averaged TOMS values exhibit a more favorable agreement with ground-based values, with typical reduction factors ranging from between 0.61--0.77, with a typical standard deviation of <0.05 from the ideal.