  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.
