I wouldn't say that it has been diagnosed - more like looked at and a few wild guesses.Update
Ive now had this diagnosed and was told it is one of the front tyres either the "run flat sensor" has fell off or broke or each wheel is set to sit on certain place and that one is meant to be elsewhere? He was unsure which. But apparently they have a sensor behind the valve? anyone had any experience of this? Because only option is dealer now because most garages wont have a clue I dont think. Anyone know if it has sensors behind the valves as well? So within the tyre I guess?
On the first gen MINIs the ABS sensor is the run flat sensor. It fits into the each hub and
has a wire running to it.
The 2nd gen MINIs use a wireless pressure sensor on the inside of the valve/tire.
As you said it's an R50 that would mean a first gen MIN CooperI. If it's a 2007 or later cooper,
then it's an R56 (2nd gen) MINI Cooper.