How would I know if I was suffering from spiritual materialism? How would I know if I was suffering from spiritual materialism as detailed in Chögyam Trungpa's book Cutting Through Spiritual Materialism? Would there be signs that I could recognise in myself and if so what would the signs be? Or is it something that is only evident to other people. Would I need to be told of my condition by a teacher or close friend?
You absolutely can recognize it in yourself. Not only can, you definitely should put effort in doing so -- it makes a huge difference in one's practice (from my own experience being a student).

Spiritual Materialism, (or we could call it Spiritual Accumulation or Spiritual Aggrandizement or Spiritual Indulging) is a tendency of samsaric mind to use spirituality (in its general sense, as an antonym of worldliness) as food for one's ego. Until the illusion of ego disintegrates, that is all the way until Enlightenment, ego uses all kinds of tricks to sustain itself, up to and including Buddhism.

Here are some of telltaling signs you are suffering from S.M. (you don't need to have them all, one is enough):


You surround yourself with Buddhist paraphernalia (tangkas, statues, prayer wheels, bumper stickers, incense, mantra CDs, tattoos, themed handbags) or you despise people who surround themselves with paraphernalia, for being too superficial;
You enjoy Buddhist workshops and lectures as socializing events, or when others enjoy Buddhist workshops and lectures as socializing events, you stay on sidelines, secretly despising everyone for not being serious about Dharma;
You are too interested in levels of realization and how yourself measure up; or you never think about levels of realization, "because advanced practitioners are above that kind of stuff".
You are eager to study obscure Buddhist philosophy and feel that understanding technicalities of Dharma makes you a better practitioner; Or you despise people who indulge in Buddhist philosophical speculation and instead take pride in being a Zen or Tantra student.
You are snappy and irritated with worldly people with their childish interests; Or you are being a super-nice or super-humble selfless holy Bodhisattva, while secretly enjoying the glow of your halo;