...it is factual, fascinating, fun and full of useful information on Bromptons.
Ignoring the amateur Andy Warhol-like book cover, David Henshaw has written a great book covering the history of folding bikes, Brompton design, the company history and guidance on maintaining a Brompton.
I would go as far as to recommend every Brompton owner, or would be owner, should buy a copy as it is a bit like a Haynes manual combined with a Glass's guide.
My own Brompton has a creak which I have warmed to, and assumed it was the springs in my Brooks saddle groaning at my 90kg, but since reading the "Using and Maintaining a Brompton" chapter I've found it is the suspension block bolt. Apparently it is easily remedied but I'm not sure I want to - I like the creak and I like the effect it has on roadies when (occasionally on my commute) I wheelsuck and they can't figure out where the noise is coming from :-)