Do I go through security again when connecting at Heathrow?

What this answer depends on

• London Heathrow; through connections versus separate-ticket journeys
• This is a Heathrow transfer procedure, not a general rule for every airport. First establish whether you are connecting on a through itinerary or arranging a separate-ticket departure. Then identify the onward flight and follow the airport’s current routing.
• A repeat security check does not, by itself, tell you whether you must enter the United Kingdom. Do not use the security requirement to infer a visa requirement or permission to leave the airport. This guide explains the connection route; a traveler’s immigration eligibility needs separate official verification.
• The useful decision is whether to stay within the signed connections process or follow an arrivals-and-new-departure process. Heathrow directs separate-ticket passengers to plan for arrival and departure procedures rather than assuming the through-transfer path applies. Taking the wrong branch can create an avoidable detour, so resolve uncertainty before following an exit sign.
• List the stages you personally need: onward boarding-pass collection, connection routing, security, any document checks, and travel to the departure area. Do not turn a walking estimate or somebody else’s experience into a guaranteed connection time. The actual itinerary and current airport instructions are the relevant inputs.
• Heathrow connecting passengers undergo security again.
• Heathrow identifies the through-transfer route with purple Flight Connections signs.
• Separate-ticket passengers are treated as arriving and departing passengers for transfer planning.