Thanks guys!
I don't know if it's light with this guy. The leaves and bulbs aren't really yellow, just a pale green. This one is sitting in a mini greenhouse on the floor of my lounge about 1.3m or 4' below a north east facing window. It's about 60cm away from the window as well - so not a lot of natural light. I supplement the light with two domestic reading lamps running a 3W LED each (nothing special, straight from IKEA). I'm learning about growing under lights so I've just been experimenting. From what I've read though, this is not a whole lot of light.
If I had to guess what the trick was, I would say constant high humidity. I have a Miltonia clowesii division that sits on my kitchen table and if it goes dry for even one day, I end up with crinkled leaves. I've also read that the Brazillian Miltonia's are very sensitive to water loss and drops in humidity, so I have perlite at the bottom of my mini greenhouse which I pour a jug of water on once a week. This keeps the humidity at 70-80%, sometimes more.
I am a complete newbie so I'm just guessing, but it's the one thing that I know has been consistent while I've been growing this guy. But who knows? Perhaps the grower I bought this from grew it under very high light previously and so has contributed to it blooming this cycle. Perhaps my growing conditions haven't influenced it to bloom at all!