Tonight I tried another hand-held panoramic stitch; this time with a focal length of 70mm. This gave much more predictable results, and helped to minimise the appearance of rain spots on the lens.
Nikon D300; Tamron 18-270mm @ 70mm; 500 ISO; f/5.6; 1/80 second. VC on.
Exclusive bonus image:
Nikon D300; Tamron 18-270mm @ 120mm; 500 ISO; f/8; 1/200 second. VC on.