  We present a clustering analysis of QSOs using over 20000 objects from the
final catalogue of the 2dF QSO Redshift Survey (2QZ), measuring the z-space
correlation function, xi(s). When averaged over the range 0.3<z<2.2 we find
that xi(s) is flat on small scales, steepening on scales above ~25h-1Mpc. In a
WMAP/2dF cosmology we find a best fit power law with s_0=5.48+0.42-0.48h-1Mpc
and gamma=1.20+-0.10 on scales s=1-25h-1Mpc. A CDM model assuming WMAP/2dF
cosmological parameters is a good description of the QSO xi(s) after accounting
for non-linear clustering and z-space distortions, and a linear bias of
b_qso(z=1.35)=2.02+-0.07. We subdivide the 2QZ into 10 redshift intervals from
z=0.53 to 2.48 and find a significant increase in clustering amplitude at high
redshift in the WMAP/2dF cosmology. We derive the bias of the QSOs which is a
strong function of redshift with b_qso(z=0.53)=1.13+-0.18 and
b_qso(z=2.48)=4.24+-0.53. We use these bias values to derive the mean dark
matter halo (DMH) mass occupied by the QSOs. At all redshifts 2QZ QSOs inhabit
approximately the same mass DMHs with M_DH=(3.0+-1.6)x10^12h-1M_sun, which is
close to the characteristic mass in the Press-Schechter mass function, M*, at
z=0. If the relation between black hole (BH) mass and M_DH or host velocity
dispersion does not evolve, then we find that the accretion efficiency
(L/L_edd) for L* QSOs is approximately constant with redshift. Thus the fading
of the QSO population from z~2 to 0 appears to be due to less massive BHs being
active at low redshift. We apply different methods to estimate, t_qso, the
active lifetime of QSOs and constrain this to be in the range 4x10^6-6x10^8
years at z~2. (Abridged).
