  We present detailed clustering measurements from the 2dF QSO Redshift Survey
(2QZ) in the redshift range 0.8<z<2.1. Using a flux limited sample of ~14,000
objects with effective redshift z_eff=1.47, we estimate the quasar projected
correlation function for separations 1<r/h^{-1} Mpc<20. We find that the
2-point correlation function in real space is well approximated by a power law
with slope gamma=1.5 pm 0.2 and comoving correlation length
r_0=4.8^{+0.9}_{-1.5} h^{-1} Mpc. Splitting the sample into three subsets based
on redshift, we find evidence for an increase of the clustering amplitude with
lookback time. For a fixed gamma, evolution of r_0 is detected at the 3.6 sigma
confidence level. The ratio between the quasar correlation function and the
mass autocorrelation function (derived adopting the concordance cosmological
model) is found to be scale independent. For a linear mass-clustering amplitude
sigma_8=0.8, the ``bias parameter'' decreases from b~3.9$ at z_eff=1.89 to
b~1.8 at z_eff=1.06. From the observed abundance and clustering, we infer how
quasars populate dark-matter haloes of different masses. We find that 2QZ
quasars sit in haloes with M>10^{12} M_sun and that the mean mass of their host
haloes is of the order of 10^{13} M_sun. The observed clustering is consistent
with assuming that the locally observed correlation between black-hole mass and
host-galaxy circular velocity is still valid at z>1. From the fraction of
haloes which contain active quasars, we infer that the characteristic quasar
lifetime is t_Q ~ a few x 10^7 yr at z~1 and approaches 10^8 yr at higher
redshifts.
