[en] A UK-ENDF/B-IV format fission product decay data file (UKFPDD-1) has been recently established. It was produced by combining an earlier UK data file, in ENDF/B-IV format, with the US-ENDF/B-IV data library and making a number of corrections in known problem areas. In order to demonstrate the quality of UKFPDD-1 it has been used with the code FISP in decay heat calculations which are compared with both other calculations and some of the recent 'benchmark' heat measurements. The UKFPDD-1 results show excellent agreement with the experimental results (better than 7% at most cooling times and often better than 2 to 3%) and consequently a significant improvement over the results from the original FISP library. A small improvement over US-ENDF/B-IV results is also found in estimating the separate beta and gamma components of decay heat. (author)