I haven't had this with IB, but with BA when a change is made to one flight that brings you below MCT, it is sometimes a few days before they pick up the need to change the other flight(s). At that point, if the change they offer you is not to your satisfaction, you should be able to call up and get a change to a reasonable alternative. As the flights are in March, I'd leave it a few days to see what they do, and if you've had no contact after 5-7 days, give them a call.

Is the LHR-MAD on BA or IB metal? If it's IB and not a widebody aircraft, you might actually make the connection as it's T4 to T4 in MAD, but probably not a risk you (or I) would want to take. I have a 60 minute connection myself from T4S to T4 next week, so I'm hoping for no major delays in getting across from T4S.