We study a possibility of constraining isotropic cosmic birefringence with
help of cosmic microwave background polarisation data in the presence of
polarisation angle miscalibration without relying on any assumptions about the
Galactic foreground angular power spectra and in particular on their EB
correlation. We propose a new analysis framework based on a generalised
parametric component separation approach, which accounts simultaneously on the
presence of galactic foregrounds, relevant instrumental effects and external
priors. We find that upcoming multi-frequency CMB data with appropriate
calibration priors will allow producing an instrumental-effect-corrected and
foreground-cleaned CMB map, which can be used to estimate the isotropic
birefringence angle and the tensor-to-scalar ratio, accounting on statistical
and systematic uncertainties incurred during the entire procedure. In
particular, in the case of a Simons Observatory-like, three Small Aperture
Telescopes, we derive an uncertainty on the birefringence angle of
Ο(Ξ²bβ)=0.07β (0.1β), assuming the standard cosmology
and calibration priors for all (single) frequency channels with the precision
of Ο(Ξ±iβ)=0.1β as aimed at by the near future ground-based
experiments. This implies that these experiments could confirm or disprove the
recently detected value of Ξ²bβ=0.35β with a significance between 3
and 5Ο. [abridged version]Comment: 20 pages, 9 figure