The cosmic microwave background (CMB) radiation was emitted when the Universe was 380,000 years old and is observed today at 2.7 K. It is a wonderful probe to study the evolution of the Universe. Tiny anisotropies in its temperature and polarization are induced by quantum scalar (density) and tensor fluctuations (gravitational waves, GW) generated during inflation, a period of accelerated expansion arising 10-35 s after the big bang. Primordial GW imprinted a unique parity-odd pattern on CMB polarization, called B-modes. Such modes, undetected as of today, are a direct probe of the poorly known physics of inflation, and main target of several forthcoming observational projects. These will be search for B-modes at large (> 10°) and intermediate (~1°) angular scales. Among such efforts, Japan is proposing a satellite project (LiteBIRD, to be launched end 20's) with contributions from EU agencies, NASA and CSA. Large angular scales are difficult to measure due to Galactic emissions and instrumental systematics, requiring careful, detailed modelling and advanced data analysis techniques. EU scientists rely on the legacy of the ESA Planck mission (2009), but improvements of analysis methods and modelling of the instruments are now required. The main goal of CMB-INFLATE is to build a community of scientists dedicated to the development of innovative analysis of large angular scale CMB polarisation data to identify the inflation mechanism. CMB-INFLATE will focus on: (1) modelling hardware developed in three continents, including polarization modulators, optical systems, and detectors; (2) the development and implementation of innovative techniques to mitigate systematics from the sky and the instrument. Such advancements will be provided by a wide-scale international consortium involving instrumentalists, data analysis experts and theoreticians. The CMB-INFLATE outcome is expected to strengthen European leadership in the field of primordial GW and connected science.