Join Date: Oct 2006
Location: London, UK
Programs: BA Gold, VS Silver, SQ Silver, IHG Plat Amb, Hilton Gold, Marriott Plat, Accor Silver, Radisson Prem
Posts: 16,873
It's not allowed for precisely the reason stated - the security officers need to check you are not concealing anything. The same reason you have to take a hat off or your coat/jacket.
Common sense I'd have thought.