Ambassador, British Airways; FlyerTalk Posting Legend
Join Date: Apr 2012
Location: Leeds, UK
Programs: BA GGL/CCR, GfL, HH Diamond
Posts: 42,964
Yes you have to go through security, there is no transfer route at LBA. Once you go through the baggage area and through customs and the one way exit, turn right and follow the terminal to the security at the far end. You should be able to use fast track security.
45 minutes will be plenty. I reckon you should be back around to the gate in no moe than 25 minutes.