I need to find a way to accompany an elderly non-English-speaking relative to the gate at London Stansted Airport. Can I buy a ticket to get through security, walk the relative to the gate and then exit back to land side? I need to understand if this is legal, or if I would be given a fine.
Typically, airlines will give you a 'Security Pass' (instead of a boarding pass) that allows you to go into the security area for that reason, up to the gate door. At the check-in, ask for it, together with the person needing your help. If you want to be sure that it will work, call them and confirm the process now, but I have done that before.
Note you will need your ID with you, and the 'Security Pass' will be printed with your name. It looks similar to a Boarding pass, but has no flight info on it.
Here are two examples that confirm this:
http://www.flyertalk.com/forum/practical-travel-safety-security-issues/1211383-can-person-no-boarding-pass-get-guest-pass-go-thru-security.html (there are lot of people that recommend buying a ticket, that is not needed. Check for 'Orion' and 'noname's post)
P.S. It is free.