Thanks for the good wishes and the advice, both are very much appreciated.
I went back to basics and made sure the IS was off in both the lens and camera which made a difference. The next step was to borrow a sturdier tripod which, allied to the switch off made an even bigger one. This afternoon I am off for a remote.
I am holding on to the the tripod for the weekend so I can try it in the field as opposed to in the garden and if the pics stay as good as they are now I will be upgrading-the Velbon is pretty light and not really designed for a lens as heavy as the Sigma.
I'll let you know later!