Our indie Jaguar specialist uses, at our behest, the said Castrol Magnatec 5W-30 in our S-type 2.7D.
Note, however, that an annual change is far better, irrespective of low mileage. Our S covers about 12K a year; lower, or much lower, mileage means that the oil is getting polluted more than with longer journey higher mileage use.
Our '07 XK V8 X150 only covers around 1000 to 1500 miles a year, but still gets oil and filter change annually.
Just saying!