If London Met wish to charge you fees, which they will do, then they become your responsibility and will not be paid by the SLC, as per The Student Support Regulations which state that in order to qualify for a fee loan, a student must be in attendance 3 months after the start of the academic year.
You mention grants, and I think you've muddled your maintenance loan and grant in one. Grant entitlement is pro-rata'd, based on the time you were in attendance, so you would have to pay some of that back straight away. There's also an issue where the SLC can ask for most of the loan to be repaid before you're earning over £15,000 (it's in the T&C's). London Met would also probably want the bursary back too, and most likely in full.