You cannot stay airside at Heathrow Airport overnight. You can however remain in the public areas and try and sleep (I wouldn't, as I would worry about my belongings getting stolen). There are no sleeping couches, just ordinary seating. If you are worried about visa requirements though, you may be exempt.

Yes, you can sleep in London Heathrow Airport (LHR) overnight, as the airport is open 24 hours, but the experience varies depending on your terminal and security status. If you have an early morning flight and have already cleared security, you may be able to stay in the airside departures area, which is generally quieter and offers more comfortable seating; however, some terminals (like T2) may close the airside area for cleaning between roughly 11:00 PM and 4:00 AM. In the landside (public) areas, sleeping options are more limited to standard benches, often with armrests that prevent lying down. Many travelers prefer the central bus station or the cafes in the arrivals halls for overnight stays. For those seeking actual rest, Heathrow offers several short-stay hotels within the terminals, such as Aerotel in T3 or the YOTELAIR in T4, which can be booked in blocks of hours. If you choose to sleep in the terminal, it is wise to bring a sleep mask, earplugs, and an extra layer of clothing, as the airport can get quite cold and bright throughout the night.