Because of the closeness of the hard and grass runways, Duxford is classified by the CAA as having a single runway and therefore "simultaneous" movements are not allowed. This is in the PPR brief and other documents. A visiting pilot should know this and act accordingly. Whether Duxford can "instruct" a go-around is another question as they are not full ATC. I believe the runways are in the course of being separated which might improve things.