You might choose one itinerary with multiple stopovers -
for example, London - Bangkok, Singapore - Manila, Manila - London.
or London - Jakarta, Jakarta- Singapore, Singapore - Kuala Lumpur, Kuala Lumpur -Bangkok, Bangkok-London.
Or, you might need to arrive in one city, but depart from another City-
for example, London-Delhi, Trivandrum/Kochi-London
Or London-Trivandrum, Male-London
Or London - Bombay, Delhi - Kathmandu, Kathmandu - London