If it were the same, ATC really wouldn't care whether it was an ILS or MLS and the BA pilots could stop cluttering the frequency with their requests!
This would be great until we need to turn one or the other off (or downgrade) for maintenance, or worse one fails unexpectedly and we have no idea who is flying which approach.
Not fail safe I'm afraid.
So what are the economic benefits for MLS at LHR.
Equals:
British Airways and NATS intend to implement the third phase of MLS operations at LHR. This reduces the spacing between aircraft flying an MLS approach in LVPs by one mile.
Capacity.