This study presents a direct method for creating bimetallic nanoparticles (Ag/Au BNPs) within a polymerizable host by a UV light process under atmospheric conditions (air, temperature and pressure). This approach offers both simplicity and efficiency by combining the photo-induced reduction of metal precursors (AgNO$_3$ and KAuCl$_4$) and the radical photopolymerisation of a polyethylene glycol diacrylate in a single step. As a result, plasmon active coatings were obtained with three different BNPs in the form of Ag-Au alloy or core-shells (Ag@Au or Au@Ag) confined in the polymer matrix, with an average diameter between 4 and 6 nm respectively. The method requires only 15 to 45 minutes depending on the desired BNPs system that were easily triggered by playing with the redox potentials of the metal pairs and small amounts (200-300 µL) of water or acetonitrile solvents used to dissolve these precursors. This control determines which metal is reduced first to form the core and which follows for the shell, or even both simultaneously for the formation of the alloy system. Moreover, double-layered systems such as Ag@Au@Ag can also be synthesised with this approach. Various advanced characterisation techniques, including real-time UV-Vis spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and transmission electron microscopy (in particular STEM-HAADF imaging and EDS elemental mapping), were used to monitor the synthesis process and identify the formed BNPs system. These new plasmonic materials exhibit unique optical properties depending on the BNPs system, making them promising for multiple applications such as sensing, SERS, optics, catalysis or photocatalyse, and easily scalable for large-scale production.