The UCL distorted wave code. The DW code of University College London computes collision strengths and reactance matrix elements in $LS$ coupling for excitation of atoms and positive ions by electron impact in a partial wave expansion. A multiconfigurational target serves as the scatterer; the partial waves are central field solutions to a distorted wave (DW) approximation. par The DW program is run by linking two source codes: program COLALG and a modifying module called DWMODS. In stand-alone mode COLALG creates a file to the requirements of the electron collision program IMPACT, passing on target data and the angular expansion coefficients of collisional symmetries. Linked with DWMODS the program writes a reactance matrix file directly readable by JAJOM; the output file OMEGA is compatible with a similar file created by the QUB $R$-matrix code. Collisional details can be extracted depending upon the printing level. par The UCL macro-processor with the source codes as input creates FORTRAN 77 files; apart from replacing size parameters it switches parts of code on and off depending upon directives.