The electronic system developed for the SpaCal lead/scintillating-fibre calorimeters of the H1 detector in operation at the HERA ep collider is described in detail and the performance achieved during H1 data taking is presented. The 10 MHz bunch crossing rate of HERA puts severe constraints on the requirements of the electronics. The energy and time readout are performed, respectively, with a 14-bit dynamic range and with a resolution of ∼0.4 ns. The trigger branch consists of a nanosecond-resolution calorimetric time of flight for background rejection and an electron trigger based on analog 'sliding windows'. The on-line background rejection currently achieved is ∼10 6. The electron trigger allows a low-energy trigger threshold to be set at ∼0.50±0.08 (RMS) GeV with an efficiency ⩾99.9%. The energy and time performance of the readout and trigger electronics is based on a newly developed low noise ( σnoise∼0.4 MeV) wideband ( f⩽200 mHz) preamplifier located at the output of the photomultipliers which are used for the fibre light readout in the ∼1 T magnetic field of H1.