Well that's all fine and dandy, but if BA insisted it was LGW on Monday instead of LHR on Sunday, BA would in addition to the higher rate of EC261 (250€) but would also have the duty of care costs as well, so a night in a hotel plus food, plus drink, plus communication expenses, plus travel to and from hotel. Furthermore, if anyone tested this in court, and I doubt BA would want it tested, I can't see that T&C provision would stack up given clauses 2.h, 3.1.b, 8.1.b and 15.1.