In this study, high-order harmonic generation was investigated under the combined influence of three enhancement schemes: a plasmonic-enhanced two colour field, modulated polarization gating, and a static electric field. Numerical simulations based on the one-dimensional timedependent Schrödinger equation (1D-TDSE) were carried out to analyze the influence of field inhomogeneity, polarization modulation, and electron trajectory control on harmonic spectra. The analysis demonstrates that an increase in the inhomogeneity parameter, together with precise tuning of the polarization angle, produces extended harmonic cut-offs and more intense bursts near peak field cycles. The introduction of a static electric field further improved the harmonic conversion efficiency, while the combined application of all three mechanisms yields harmonic spectra characterized by two distinct plateaus, broadened spectral bandwidths, and significantly higher emission yields. A high harmonic cut-off reaching the 600th order is observed in the first plateau, while the second plateau extends beyond the 1550th order. Timefrequency spectrograms reveal well-defined harmonic bursts and high-energy electron recollisions contributing to this extension. These findings confirm that the synergy of polarization gating, plasmonic field enhancement and static field confinement offers a robust pathway for generating bright and broadband extreme ultraviolet (XUV) continua, which are essential for advancing attosecond pulse generation and ultrafast spectroscopy