I haven`t heard of the case, but there are only a few reasons we would go with two I/O`s
Firstly, when we have a new inspecting officer who is either shadowing another officer or one who is being monitored for development needs. Although, we do agree this with the RP prior to inspecting.
Secondly, following an inspection where the I/O is considering prohibition - The purpose of this is usually to the advantage of the RP as the additional officer is required to ensure that all possibilities have been considered. Let`s face it we can all get so focused on one problem we can miss the obvious solution.
Finally, I have used two I/O`s when we have awkward or aggressive RP`s. I can think of one particular head of a local independent boarding school who would try to divert your attention at the critical moment. We used to have one I/O to engage in conversation and the other do the inspection.
Is it really such a problem if the RP only wants one I/O to inspect, have you seen how many biscuits some of my colleagues eat.