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 £299! This is a price for round-trip incl. all charges and checked luggage. Flights are also available at the end of March 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 departing from London between 1st of January till first half of March then May to 30th of June 2018. Max stay 4 months. Valid for bookings made till end of October 2017. If interested in this solution you can refer below to our booking sample and few travel dates. Based on similar logic you may also consider to fly to India already from £237.
Booking sample
London - Istanbul - Kathmandu - London from £299
Travel samples
13.1. - 15.1. - 27.1.
5.2. - 7.2. - 24.2.
5.3. - 7.3. - 19.3.
10.3. - 12.3. - 22.3.
12.3. - 12.3. - 26.3..
30.5. - 1.6. - 11.6.
5.6. - 7.6. - 25.6.
Booking sample of cheap Multi-city flights from London to Nepal + Istanbul from £299 here. In this case you would fly from London to Kathmandu on 12th of March. Your return flight from Nepal back to Europe would be on 26th of March 2018.