There is no CAA inspection requirement for IFR, but the aircraft itself must not have a VFR-only or VMC-only restriction in its operating handbook.
I am not certain about the status of a BRNAV GPS though - this is required for airways flight (FL095 and above). This might need an inspection, on a G-reg. On an N-reg, an IFR GPS requires an FAA-stamped aircraft manual supplement before it can be legally used for IFR.