Not really - had you already taken a postgraduate Masters course then starting an MSc might look like you were just trying to collect qualifications. As that isn't the case, the MSc might be worthwhile. However, in our opinion, it would only be a better option to the MPhil if:
a. It is very unlikely your MPhil registration being changed to a PhD
b. You don't want to do a PhD
c. You want to do a PhD, but in a different lab/department/university
Bear in mind that we don't know very much about your specific situation, canvas as much opinion as you can.