There is always a ton to do in London, people to see, festivals to check out, old friends to catch up with, and new adventures to find.
Since London is a common layover stop in transatlantic flights and flights through Europe. It is always an easier place to find a stopover when flying past or through Europe because London has four major airports. However, more airports do increase the complexity of the search.
With that complexity, your best bet is to accomplish a cheap stopover to London is to use Hopupon.com. Hopupon will search 1000's of combinations to find the best deals for a stopover in London. It will also give you some other city suggestions in case you want to try somewhere new!
On the odd chance that London does not come up for you (likely it's not a cheap stopover for your route). There are ways you can get there manually, but it will take a bit of patience and resilience.
Doing it on your own
Your best deals for stopovers will require a bit of muscle to find the best prices and even more stamina for some local or domestic routes as not all airlines are on every Online Travel agency (OTA). The airlines that might not be on some OTA's usually include discount or regional airlines, which often have the lowest prices. If your flight route might contain one of these airlines, you'll need to do a bit of additional research.
Examples of this in the North American market areas such
• Delta Air Lines: Excluded from Cheapair, CheapOair, TripAdvisor
• Southwest: Tickets only available for purchase on the Southwest website (or over the phone)
• JetBlue: Excluded from Vayama, SmartFares, MyFlightSearch
• Frontier: Promotions only bookable on Frontier's website.
• Spirit: Promotions only bookable on Spirit's website
• Allegiant: Excluded from Vayama, Expedia, Orbitz, Priceline, MyFlightSearch, Cheapair, CheapOair, OneTravel, and others
In all cases, the general process is the same. For a stopover in London, I will share an example of finding a London stopover on a New York and Bangkok flight.
Know your surrounding airports
First, you need to research the surrounding airports to the point where you would draw the line on the distance to saving.
New York City has three main airports: JFK, LaGuardia, and Newark (technically New Jersey). Other International airports that fly to Europe that you might want to consider are Philadelphia and even Boston if the price is right. Even if it's only slightly less, maybe it's an excellent excuse to make a quick stop in either of those cities.
If the stopover city is domestic in relation to the departure city, I would add in other airports such as Harrisburg, Lehigh Valley, Scranton so you can expand your search to find the best deal/adventure.
To find all the surrounding airport options, a quick google map search with the keyword 'airport' can help you find additional airports that may contain cheap flights.
For the stopover city, London, you will do the same. Since we are flying to Bangkok, likely the main airports listed above will do.
However, if our final destination was in Europe, there are 5-10 more airports we could look at including, East Midlands, Birmingham, Nottingham, Bournemouth, Bristol, and Norwich airport. Some of them are a few hours away from Lond, but this is an adventure, see somewhere new!
At the arrival city, it's probably safe to search the main airport in Bangkok, Suvarnabhumi, but it's hard to rule out Don Mueang. Again, if your stopover city was something closer, you might want to add Chaing Mai, Yangon, and Phuket to your airport list to add to the adventure and lower the price.
Creating the search options
The first step is to list all the airports in all three cities, New York, London, and Bangkok, and then try every combination. It would better to only search flight paths with direct flights, and if none do at most one layover. You can easily find this out by looking at the wiki for that airport. They always list all direct flights offered.
From our example, we can guess that only some airports have direct flights between New York and London and others London to Bangkok, which means we can remove airports that don't have direct flights. We can remove Gatwick airport because it doesn't have a direct flight to New York or Thailand from London.
An example of a route list is as such,
LaGuardia, Heathrow, Heathrow, Suvarnabhumi
Newark, Heathrow, Heathrow, Suvarnabhumi
Newark, Stanstead, Heathrow, Suvarnabhumi
Search all combinations
A quick hack to speed up the process is to use metro Codes instead of airport codes. Metrocodes will search all airports in a city. Each OTA could have different metro codes they support and are defined. Examples of well-used metro codes in OTA's are New York, NYK, London LON, and Bangkok BKK.
It would be best if you searched all the flight route combinations to find the best price. In addition to switching up the airports, you'll want to switch up the dates as well. In some cases, a difference in a day can be over 100 dollars in savings.
If your favorite OTA has a nearby airport button or +- 3 days button, these buttons will dramatically speed up the search process.
How do you know when to search individual airlines.
A way to know if you're missing an airline is to look up discount airlines for the country you're flying from or to, and if they don't appear in the search results of your favorite OTA, then likely it is because that OTA does not connect with that airline.
If this is the case, you need is to search flights directly with that airline or switch OTAs to find out if that option is the best price.