Originally Posted by corporate-wage-slave

If you are only ticketed LHR-SIN, so the other sectors are on a separate ticket, then this is just a risk which didn't work out. BA will doubtless offer a rebooking on the same day BA15, or the previous day, or other days - so that means they would have done the rebooking options, or offer a refund to contribute to your SQ replacement flight. If the booking was LHR-LPQ then a different set of logic would apply.