A key and descriptions are given for the identification of British polycentropid larvae. Early Continental descriptions include the Holocentropus and Cyrnus species which occur in Britain, but a consideration of British material has indicated that some changes are required in the characters used to separate these species. In both Polycentropus flavomaculatus and Holocentropus species the anal claws are right-angled. It has been reported that P. flavomaculatus has only one dorsal spine on the anal claw and differs from Holocentropus where there are at least two such spines. Re-examination of P. flavomaculatus larvae has shown that the anal claw bears two dorsal spines. The previously unknown larvae of Polycentropus kingi and Polycentropus multiguttatus are described. These two species, unlike P. flavomaculatus, have obtuse-angled anal claws, and in this respectresemble Plectronemia. A new character based on the relative lengths of the prothoracic tibia and tarsus has been introduced to separate the three Polycentropus species from Holocentropus and Plectroenemia. The previously unknown larvae of Plectroenemia geniculata have been examined and differ from P. conspersa in the arrangement of bristles on the last abdominal segment and in the pigmentation of the labrum.