I?m planning to start my MBA this year.
I have 2 options until now . One university is AMBA accredited (BRUNEL). The other option is not(MIDDLESSEX)..
Is an AMBA accreditation really important in selecting an MBA university in UK?

Thank you very much

You will get some minimum guaranty for the quality of your course.

Unfortunately, both schools that you listed down are NOT top MBA programs in London....

Maybe you could look at a school like London Business School? That might give you an indication to what a top MBA program in London is like.