  We show that an inflationary slow-roll potential can be derived as an IR
limit of the non-perturbative exact renormalisation group equation for a scalar
field within the mean-field approximation. The result follows without having to
specify a Lagrangian for the UV theory at the Planck scale. We assume that the
theory contains a scalar mode with suppressed coupling to other UV fields, and
that higher derivative couplings are suppressed. The resulting effective
potential gives rise to slow-roll inflation, which is fully consistent with the
recent observations. As an example of how the proposed renormalisation group
procedure works, we perform an explicit calculation in the $\phi^4$ theory.
