We present optical (similar to 3200 to similar to 9000 Angstrom) off-nuclear spectra of 26 powerful active galaxies in the redshift range 0.1 less than or equal to z less than or equal to 0.3, obtained with the Mayall and William Herschel 4-m class telescopes. The sample consists of radio-quiet quasars, radio-loud quasars (All with -23 greater than or equal to M-V greater than or equal to -26) and radio galaxies of Fanaroff-Riley Type II (with extended radio luminosities and spectral indices comparable to these of the radio-loud quasars). The spectra were all taken approximately 5 arcsec off-nucleus, with offsets carefully selected so as to maximize the amount of galaxy light falling into the slit, whilst simultaneously minimizing the amount of scattered nuclear light. The majority of the resulting spectra appear to be dominated by the integrated stellar continuum of the underlying Salaries rather than by light from the non-stellar processes occurring in the active nuclei, and in many cases a 4000-Angstrom break feature can be identified. The individual spectra are described in detail, and the importance of the various spectral components is discussed. Stellar population synthesis modelling of the spect ra will follow in a subsequent paper.