The best time to book cheap flights to London can vary, but there are some general tips that might help you find better deals:

Book in Advance: In general, booking your flight well in advance can often result in lower prices. Aim to book your tickets at least a few weeks ahead of your travel date.

Midweek Flights: Flights tend to be cheaper if you can travel on Tuesday or Wednesday. Avoid weekends if possible, as they are popular for both leisure and business travel.

Off-Peak Seasons: Traveling during off-peak seasons can also lead to cheaper flights. Try to avoid peak travel times, such as holidays and school vacation periods.

Set Price Alerts: Use online tools and apps to set price alerts for your desired route. This way, you'll be notified when prices drop, allowing you to book at the optimal time.

Flexibility with Dates: Being flexible with your travel dates can make a significant difference in the cost of your flight. Use flexible date search options to see if there are cheaper options on neighboring dates.