There is a transit visa available (if you're not eligible for VOA) but the rules for it are slightly odd, and, from experience, it confuses both consular staff and immigration officers. It does save you money vs a tourist visa, but check you have the paperwork to hand on arrival, check the time windows for application (which are fairly short) and be prepared to be patient as they ask a supervisor for help...
There is a near zero chance that Air Asia will check luggage through to BA. And you may well face problems reentering the terminal in the early evening for a morning flight.