Swift heavy ion (SHI) irradiation of P(VDF–HFP)–(PC+DEC)–LiClO₄ gel polymer electrolyte system with 48 MeV Li³⁺ ion having five different fluences were investigated with a view to increasing the Li⁺ ion diffusivity in the electrolyte. Irradiation with SHI shows enhancement of conductivity at lower fluences and decrease in conductivity at higher fluences with respect to unirradiated polymer electrolyte films. Maximum room temperature (303 K) ionic conductivity is found to be 2.2 × 10⁻² S cm⁻¹ after irradiation with fluence of 10¹¹ ions cm⁻². This interesting result could be ascribed to the fluence dependent change in porosity and to the fact that for a particular ion beam with a given energy higher fluence provides critical activation energy for cross linking and crystallization to occur, which results in a decrease in ionic conductivity. XRD results show a decrease in the degree of crystallinity upon ion irradiation at low fluences (⩽10¹¹ ions cm⁻²) and an increase in crystallinity at high fluences (>10¹¹ ions cm⁻²). Analysis of FTIR results suggests the bond breaking at a fluence of 5 × 10¹⁰ ions cm⁻² and cross linking at a fluence of 5 × 10¹² ions cm⁻² which corroborate the conductivity and XRD results. Scanning electron micrographs exhibit increased porosity of the polymer electrolyte films after ion irradiation.