New neutrino–nucleus interaction cross-section measurements are required to improve nuclear models sufficiently for future long baseline neutrino experiments to meet their sensitivity goals. A time projection chamber (TPC) filled with a high-pressure gas is a promising detector to characterise the neutrino sources used for such experiments. A gas-filled TPC is ideal for measuring low-energy particles, which travel further in gas than in solid or liquid detectors and using high-pressure increases the target density, resulting in more neutrino interactions. We examine the suitability of multiwire proportional chambers (MWPCs) from the ALICE TPC for use as the readout chambers of a high-pressure gas TPC. These chambers were previously operated at atmospheric pressure. We report the successful operation of an ALICE TPC outer readout chamber (OROC) at pressures up to 4.2 bar absolute (barA) with Ar-CH4 mixtures with a CH4 content between 2.8 and 5.0%, and so far up to 4 bar absolute with Ar-CO2 (90-10). The charge gain of the OROC was measured with signals induced by an 55Fe source. The largest gain achieved at 4.2 bar was (29±1)·103 in Ar-CH4 with 4.0% CH4 with an anode voltage of 2975V. In Ar-CO2 with 10% CO2 at 4 barA, a gain of (4.2±0.1)·103 was observed with anode voltage 2975V. We extrapolate that at 10 barA, an interesting pressure for future neutrino experiments, a gain of 5000 in Ar-CO2 with 10% CO2 (10,000 in Ar-CH4 with ∼4%CH4) may be achieved with anode voltage of 4.6kV (∼3.6kV).