Hello there, and welcome to Flyertalk Ms_KH, welcome to the BA forum in particular. I hope you have a good trip ahead to London. Please continue posting here, it's thanks to questions like this that this resource is worthwhile. I think your questions have been answered, I would certainly start with the BA App/BA.com first at 24 hours before departure and then try Qantas if that doesn't work. And 110 minutes is fine at SYD, gives you pretty much an hour spare if all goes to plan.