PhD to MPhil - not enough substantial work? what does it mean?

T

I've always heard that if you don't have a 'substantial' amount of work, you'd be downgraded to an MPhil, but what does 'don't have substantial amount of work' mean?
Can a 300-500 page thesis be downgraded to an MPhil? I know it's not about the quantity but more of the quality, but 300-500 page of thesis should have a considerable amount of novel discussion and output.

C

I could easily write 300 - 500 pages of b*llshit.. :P

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