Dates? 2 people presumably? The problem is the Male to Mahe flights, it's substantially cheaper to book LHR-MEL, MEL-MLE, SEZ-LHR and then tack on a MLE-SEZ flight separately. For this, I get it to price out at around 3000 GBP. If you instead do MLE-LHR, it prices out around 2200 GBP. Of course, there are additional costs for the MLE-SEZ(-MLE) flights, but still substantially cheaper.