I've seen a few additional questions about this so thought I would post a brief update.
I took the van into ford who on instruction replaced the receiver in the cab which fixed everything. I can't tell you much about the process as I obviously wasn't there, but they didn't take out all the headliner and overhead compartment so it seems to me to be a relatively straightforward fix. Other people on this thread have posted the location of the receiver so I'd recommend you take a look there.
Although it was some time ago it was a painful process because Ford don't like doing as you tell them, and I've since had 2-3 additional bad experiences with Ford so will absolutely not be using them again. I'd recommend using an independent garage.