A larva of the harlequin ladybird, Harmonia axyridis (Coleoptera: Coccinellidae).
The following is a pupa which I think is of the same species, the spikes are apparently characteristic.
And this, I think this a more mature pupa of this species:
And this is an adult of this species:
The adults of H. axyridis are very variable in colour and pattern, see here for some illustrations.
Photos taken in Whiteknights Park, Reading University grounds on 2009-05-10, 2009-09-24, 2009-07-16, and 2009-05-10, respectively.