Yes, Why Did Derry Irvine Rebel?

Last night's legislative licking in the Lords over the government's terror Bill will have been a surprise to few (well, the Labour whips perhaps) but the erstwhile Lord Chancellor's decision to rebel against his own party could be seen as significant, as the Guardian do attest.

Need to know:
i) once had a whole book written against him and his policies
ii) caused some amusement among his former civil servants when spotted looking rather dishevelled on an early morning bus in Lambeth only days after his resignation
iii) angled to become Lord Warden of the Cinque Ports as a post-Cabinet sinecure and didn't

The last point might explain his recent discovery of the finer points of political defiance.