The Student Room Group
Reply 1
Yes you could be considered for a Phd at Cambridge. I read this somewhere on the website. Basically you would have to finish amoung the very best. I think the fact that they would consider MPhil student is important since sometimes with these kind of programes it is the case than you cannot apply to the same university for a Phd.
Reply 2
But they have explicitly mentioned that to pursue a PhD, you should enrol in MPhil Financial Research.

Previously I know they did take in students from MPhil Finance as it was the only Finance masters. However, they have since created a new MPhil to cater to PhD aspirants.
But with an intake of 2-4 per year, it's not possible to do a PhD in JBS.

One of the criteria to the PhD programme is to have a substantial research thesis in a relevant masters. MPhil Finance is solely coursework.

So I'm not too sure if they'll take you in. Unless like you said, the top student of the programme.
Reply 3
If you graduate top of the class in the MPhil Finance, ot let's say top 3, I'm pretty sure they would offer you a PhD spot if you want one. That's my guess.

But of course that would mean an additional 3 years (not 2 as the year doing course work would not count).
Reply 4
I know people with the MPhil in Finance who have done a PhD.

This is from the JBS website: "Some graduates of the MPhil in Finance have joined the PhD programme at Cambridge or proceeded to a doctoral programme elsewhere. MPhil in Finance students will take three further years to complete their residence requirements for the Cambridge PhD."

from http://www.jbs.cam.ac.uk/programmes/mphil_finance/careers.html