In the same situation Kimmy and I have decided to wait for the budget as a good saving could be had making the Cooper D around the same price and the Cooper. On top of that cheaper running costs would make the Cooper D a great way to reduce motoring costs and do our bit environmentally. If the government don't do anything I will order after the budget and have lost nothing waiting around 8 weeks.
The King Report Part 2 will give us a good indication of the UK Government's intention if this is ready before the budget (fingers crossed). Part one is available here:
http://www.hm-treasury.gov.uk/media/...07_king840.pdf and gives strong indication of what will be in part 2 in terms of the general public being given incentives to purchase cars with greener technology/figures.