Current model designations

I may be going senile or just thick but can anyone explain the current McLaren model designation logic and what the actual numbers refer to?

I should have added that it looked to me as though numbers refer to the BHP rating and letters the body style/type?
But that certainly does not apply to the MP4/12?

They said on top gear that the MP4-12C is named after a fax machine... honestly, I wouldn't be surprised because the numbers in the name are not relevant in any way I can think of.

The explanation for the MP4-12C's name can be found here:

https://www.youtube.com/watch?v=qLV3Qi4hM40

>8^)
ER