If I had seen this post earlier I would have pointed you in that direction. I bought an 05 R52 Mini Cooper S that would not come up to temperature and I discovered an operational thermostat that had been fitted (vis-a-vis the gasket) incorrectly and water was simply getting past the thermostat all the time. Easy fix in the end.Ok so a quick update.
And it's good news, took the car back to garage Monday night for then to check Tuesday, they took the pipes of drained the car and refilled, test drove it and still the same thing. So Wednesday they took the T stat out replaced that with another new one and refilled again. Success the gauge now warms up to the middle within a couple of miles and hot air blowing within a few hundred yards.
It was all down to a faulty new stat.
Thank you guys for helping diagnose the problem and messaging with what it could possibly have been.
Wishing you all a merry Christmas.