OK, so that was easier than expected.
For reference:
Once the car is off the ground and the wheels have been removed:
1) Remove the undertray by removing the 6 x 10mm bolts (very easy)
2) Undo the antiroll bar clamps (two 13mm bolts on each side)
3) Undo the drop link bolts (17mm) on each side.
4) using fairy liquid to lubricate, slide the bushes off the antiroll bar
5) Fit the new bushes into the new clamps
6) Slide the bushes onto the antiroll bar
7) Apply the new drop links onto the ends and bolt them into place

In order to get the antiroll bar up into position so that the clamps can be bolted into place (the 13mm bolts), I needed to use another jack pushing upwards on the antiroll bar.
9) Bolt the clamps into place
All good. Whole operation took about an hour, including faffing.
Not bad, given that an OPC had quoted me GBP250 just to replace the clamps and bushes (price didn't include the drop links).