Jet2.com and Jet2holidays have further hiked capacity from Stansted by deploying a 16th aircraft during the summer peak.
The expansion comes as twice weekly flights are added to Bourgas in Bulgaria from July 21 until late September.
The new flights will serve the Black Sea coast as well as resorts, including Sunny Beach, Nessebar and St Vlas.
The 16th aircraft will add thousands of seats to destinations in the Balearics, Italy, Portugal and Greece during the school holidays including Majorca, Ibiza, Menorca, Sicily, Faro, Crete, Kalamata and Rhodes.
This follows a 10% year-on-year increase in summer availability from Stansted unveiled last week with the addition of a 15th aircraft and new routes to Athens and Rome to give more than 2.1 million seats.
Chief executive Steve Heapy said: “The demand from customers and independent travel agents has remained strong for several months, so we have once again responded by expanding our programme and investing in our London Stansted operation.
“As a result, customers and independent travel agents now have more choice, more destinations and more sunshine to look forward to.”
The airport’s aviation director Simon Gorrighan added:“The addition of a 16th based aircraft by Jet2.com and Jet2holidays at London Stansted this summer season is fantastic news for passengers looking to take advantage of the extra choice and extra destinations now on offer, including the introduction of exciting new flights and holidays to Bourgas in Bulgaria.
“The news is a real vote of confidence in the airport and a reflection of the huge demand from passengers across the region for great value, convenient flights and holidays.”