Amber Alert just mean higher vigilence required by all.
I understood that TfL used "amber alert" to mean full evacuation of all trains (via next station), presumably "red alert" means all trains stop immediately.
EDIT: "Code Amber" does have this meaning, Andrew Winstanley [BBC]has just said TfL "...called Code Amber on those lines" which might explain the confusion
Sky News are being totally irrisponsible. THe reports they're now claiming as fact (nail bomb, gunshots etc) are pure speculation, and at the moment, appear to be untrue.
Listen to 5 Live for proper coverage, and not unconfirmed crap.
Actually, Reuters have been heard to report that there was a nail bomb as well - and did say something about gunshots too.
I'm just wondering - had today's cricket match been at The Oval instead of Lords, what would have happened then?