G-XLEH British Airways A388

BA flight 293 bound for Washington Dulles Airport dumping fuel over Wales after turning back around from Ireland due to a incessant fire alarm in one of the lavatories. Fire crew boarded the aircraft after emergency landing at Heathrow and declared it safe. Engineers failed to fix the problem while pax were kept waiting inside the aircraft for 2 hours. Eventually, the flight was cancelled and pax were left to fend for themselves - some stranded in London for 2 or 3 days due to unavailability of seats.