Well, thanks for the feedback. After a number of people explained I was being insane, and probably guaranteeing that I’d herniate something, I decided not to bring the bike home. At first the kind folks here offered to sell it for me via that finest of NZ institutions, trademe.co.nz… Then it turned out that my boss wanted to buy a bike anyway, and offered me a good price too. So, given the fact that I’d have to have bought a much larger bag for everything else, and could quite easily been hit for a fair chunk of import duty, the amount I’m losing on selling the bike and buying a new one in Britain is pretty insignificant.
So now I only have everything else to sort out. Yay.