  The inclusive and fiducial $t\bar{t}$ production cross-sections are measured
in the lepton+jets channel using 20.2 fb$^{-1}$ of proton-proton collision data
at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the
LHC. Major systematic uncertainties due to the modelling of the jet energy
scale and $b$-tagging efficiency are constrained by separating selected events
into three disjoint regions. In order to reduce systematic uncertainties in the
most important background, the W+jets process is modelled using Z+jets events
in a data-driven approach. The inclusive $t\bar{t}$ cross-section is measured
with a precision of 5.7% to be $\sigma_{\text{inc}}(t\bar{t})$ = 248.3 $\pm$
0.7 (stat.) $\pm$ 13.4 (syst.) $\pm$ 4.7 (lumi.) pb, assuming a top-quark mass
of 172.5 GeV. The result is in agreement with the Standard Model prediction.
The cross-section is also measured in a phase space close to that of the
selected data. The fiducial cross-section is $\sigma_{\text{fid}}(t\bar{t})$ =
48.8 $\pm$ 0.1 (stat.) $\pm$ 2.0 (syst.) $\pm$ 0.9 (lumi.) pb with a precision
of 4.5%.
