More people will have encountered Titan Airways this year than ever before. This is due to TUI using them to operate flights this summer. They have been unable to fulfil demand themselves this summer.
Titan Airways are based at Stansted and have been operating since 1988. They have a small number of aircraft that operate both cargo and passenger flights, focusing on private charter or leased charter to other airlines. A lot of this is commercial or private hire or short turnaround lease to other airlines when operational need arises.
This summer TUI have a number of their own 737 aircraft out of action due to the grounding of these aircraft and have used Titan to operate a number of flights from Stansted so they can then use their own aircraft from other UK airports.
If you have booked with TUI and flying from Stansted do not be surprised if they notify you that your flight will be operated by Titan. They are using Titan staff plus TUI stagg onboard and offering the normal TUI food, drink and duty free service on board.