An analytical framework is presented to understand the effects of a fluctuating intensity of the cosmic ionising background on the correlations of the Ly{alpha} forest transmission fraction measured in quasar spectra. In the absence of intensity fluctuations, the Ly{alpha} power spectrum should have the expected cold dark matter power spectrum with redshift distortions in the linear regime, with a bias factor b_{delta} and a redshift distortion parameter {beta} that depend on redshift but are independent of scale. The intensity fluctuations introduce a scale dependence in both b_{delta} and {beta}, but keeping their product b_{delta}{beta} fixed. Observations of the Ly{alpha} correlations and cross-correlations with radiation sources like those being done at present in the BOSS survey of SDSS-III (Busca et al. 2013; Slosar et al. 2013; Font-Ribera et al. 2014) have the potential to measure this scale dependence, which reflects the biasing properties of the sources and absorbers of the ionising background. We also compute a second term affecting the Ly{alpha} spectrum, due to shot noise in the sources of radiation. This term is very large if luminous quasars are assumed to produce the ionising background and to emit isotropically with a constant luminosity, but should be reduced by a contribution from galaxies, and by the finite lifetime and anisotropic emission of quasars.
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