Experimental research facilities involving critical assemblies used in support of the U.K. nuclear power program are reviewed from the perspective of nuclear criticality safety. The scope of the U.K. program is outlined, and major facilities and programs are briefly reviewed. The methods and data arising from these programs, and their application for nuclear criticality safety assessment, are noted. The experiments selected for inclusion in the International Criticality Safety Benchmark Evaluation Project "International Handbook of Evaluated Criticality Safety Benchmark Experiments" are briefly outlined.