I came across this theorem here:https://cameroncounts.files.wordpress.com/2014/12/lect2n.pdf. However it is stated without proof and I'm not really sure where to start, any hints would be appreciated!
Let $G$ be a transitive but imprimitive permutation group on $Ω$. Let $Γ$ be a block of imprimitivity, and $H$ the permutation group induced on $Γ$ by its setwise stabiliser; let $∆$ be an index set for the set of blocks of imprimitivity, and let $K$ be the permutation group induced on $∆$ by $G$. Then there is a bijection between $Ω$ and $Γ × ∆$ under which $G$ is embedded as a subgroup of $H \wr K$ (with its imprimitive action).