Irredundant bases for soluble groups

Let $Δ$ be a finite set and $G$ be a subgroup of $\operatorname{Sym}(Δ)$. An irredundant base for $G$ is a sequence of points of $Δ$ yielding a strictly descending chain of pointwise stabilisers, terminating with the trivial group. Suppose that $G$ is primitive and soluble. We determine asymptotically tight bounds for the maximum length of an irredundant base for $G$. Moreover, we disprove a conjecture of Seress on the maximum length of an irredundant base constructed by the natural greedy algorithm, and prove Cameron's Greedy Conjecture for $|G|$ odd.