Can I exit the airport after going through security? Once through security, there is no way to exit the airport before getting on your flight, except in the case of significant flight delay, where airport staff will be on hand to support you.

Yes, you can technically leave a UK airport after passing through security, but it is a logistically complex process. Unlike some European airports, UK terminals are not designed for "exit-and-re-entry." If you decide to leave (perhaps due to a very long delay or a change of plans), you must be escorted back through the "Arrivals" channel by a member of airline staff or airport security, which can take a significant amount of time. You will effectively be "importing" yourself back into the UK, meaning you must clear Passport Control and Customs again. When you return to catch your flight, you will have to undergo the full security screening process from scratch. It is generally not recommended unless your layover is longer than 6–7 hours and you are prepared for the intensive transit and security requirements of London or Manchester hubs.