Without wanting to sound harsh, £1200 is only 8-10 hours, you can't do a lot of fault-finding across multiple systems in that time, most of those hours will be spent removing trim, seats etc. and finding out what it isn't. It does sound like it could be either rodent damage or water ingress, fault codes won't necessarily help in those circumstances, only the mk.1 eyeball - and that takes time and experience, the fix may well be a 30 minute harness repair (plus refitting the trim etc.) Conversely, it may be a gateway module (there are several) that is faulting and dropping communications between systems - again, difficult to identify as you need to be monitoring the exact module at the exact time it faults - and then find out if it's an internal defect, poor electrical contact or a deteriorating cable joint causing low voltage. Realistically, you need to set yourself an upper limit for diagnostics - and have a 'plan B' if that limit is reached before a fix is identified. Simply having it taken to another repairer will only incur parallel costs as they'll start at the beginning again.
It does sound like they're doing things properly as you haven't mentioned 'they're replaced this & that, which hasn't fixed anything' so there's probably someone there that knows their trade without resorting to the 'parts cannon' as a diagnostic aid.
they tried to say it may be rodents. But can't be sure any one got any ideas 
