Booking some interesting multi-city flights from London to Nepal and Istanbul at once is possible with Star Alliance member Turkish Airlines. Such a routing is now possible to purchase already for £278! This is a price for round-trip incl. all charges and checked luggage. Flights are also available at the end of April which is one of two main seasons for hiking in Nepal and considered as best time to visit this beautiful country.. To reach the lowest fare you have to book your multi-city ticket with at least two nights in Turkey on your way to Kathmandu..
If interested in this deal with Turkish Airlines look for flights in January and February then between end of April and 11th of July 2017. Max stay 4 months. Valid for bookings made till end of December 2016.
Booking sample of cheap Multi-city flights from London to Nepal + Istanbul from £278! In this case you would fly from London to Kathmandu on 26th of March. Your return flight from Nepal back to Europe would be on 8th of April 2017.