Flight tickets to London are typically cheapest during the off-peak travel months, especially January, February, and sometimes November. These periods fall outside major holidays and summer tourism spikes, so airlines often offer better deals to fill seats. Booking 6–8 weeks in advance and being flexible with your travel dates (like flying mid-week) can also help lower the cost.
Interestingly, I came across a post by expert estate agents who often assist international clients relocating to London they mentioned that these months not only offer cheaper airfare but also more housing availability, making it a strategic time for those moving or planning long-term stays in the city.