We have done all of the things mentioned below, but to no avail, the heater appears to be working, but no heat is getting in to the cabin, surely someone else has had this problem and managed to fix it ??

I’m having same problem, did anyone ever get to the bottom of it please?

Mine does exactly the same, just stops being warm after a while unless you turn the temp up a few degrees Geoff

If you have the auxiliary fuel fired burner heater (FFBH) (standard on the SDV8) it's more than likely the coolant diverter valve on the bottom of the unit. Easy change and not too expensive. Easy check is feel the temperature of the 2 hoses going up to the EGR, if they are dissimilar, then that's definitely your problem. L405 SV Autobiography LWB SDV8, finished in Aston Martin China Grey by ETO division.