No problem. The baggage services (I think it's called) is located at the far international arrivals area of the arrivals floor plate. Next time you're in arrivals, if you look at the lift steelwork it's actually colour coded. The room you need is near the red lifts. It's quite difficult to see as it's just a sign above a door.

You simply walk in and it's a staff search area to get airside. There's a telephone - you tell the security folk that you've come to collect a bag and they'll tell you to press redial on the phone. That goes through to a BA rep who comes to meet you. You go through security as you would for a normal flight and then the rep takes you through.

I had no issue whatsoever. There were plenty of bags in the locality too when I went through to identify mine.