If your flight is from MCO-LGW on BA, it has not been changed from a 747 to a 777, because BA does not operate 747s on that route (or at all to/from LGW). It may have been changed from one 777-200 configuration to another.

The chances of a refurbished 777-200 on that route are normally pretty high, since the refurbishment programme is well advanced, but your flight currently has an unrefurbished aircraft assigned. Equipment change is always possible.