It's right on published minimum connect time (MCT); anything shorter and they shouldn't even allow you, but 90 minutes is fine.

(I don't do it often but 45 minutes is a reasonable length of time to allow - although if they only had a 45 minute MCT then one minute late would mean missing a flight in many cases, and indeed even on-time transfers would be a problem if you had mobility issues.

If it's the last flight of the day to NCL, or if it's at a time of year when there's a high risk of fog (NCL is often one of the first routes to get cut) then would your commitments on the following day allow you to spend a night at Heathrow (at BA's expense?)