  Absorption spectra of high redshift quasars suggest that the reionisation of
cosmic hydrogen was complete near z~6. The dominant sources of ionising photons
responsible for this reionisation are generally thought to be stars and
quasars. In this paper we make a quantitative estimate of the relative
contributions made by these sources. Our approach is to compute the evolution
of the post overlap ionising background radiation by combining semi-analytic
descriptions of reionisation in a clumpy medium with a model for the quasar
luminosity function. Our overall model has two free parameters, the star
formation efficiency and the minimum quasar luminosity. By adjusting these
parameters, we constrain the relative contributions made by stars and quasars
through comparison with reported observations (Fan et al. 2005). We find that
the relative quasar contribution (at z=5.7) to the ionising background was
between 1.4% and 14.5%. The range of uncertainty is dominated by the unknown
minimum quasar luminosity.
