LHR make you do security again even if you arrive on a BA domestic connection from MAN / GLA / EDI etc. It is extremely frustrating and time-consuming. And it only makes the travel experience 'safer' if you presume 1) that screeners at MAN / GLA / EDI perform their own thorough security search incompetently, and 2) that anybody with ill-intent would sit placidly through their first flight having successfully breached security and made it on board an airliner, then attack their onward connecting flight instead. But apparently those who organise things at LHR know better.
So the answer to you is YES. Expect a time-consuming duplicate security check, often performed by a scowling member of staff. LHR security specialises in these. Allow time to completely re-pack your bag after they've unnecessarily emptied everything out and left it in a pile.