> They had a "secure document store" built within their suite, with a thick door made of 19mm ply layers either side of a 6mm steel plate, welded to a full-length hinge, which was in turn welded to a 25mm steel tubing frame, with big long brackets bolted into the brick work of the exterior wall on one side and a steel beam on the other.

Wow, that sounds like a pretty secure entry! I wonder how they secured the walls, that’s a lot of steel plate, enough to require structural reinforc—

> So yeah it took about ten seconds to get in to the secure room. I cut a hatch through the plasterboard with a Stanley knife, recovered the keys, taped the plasterboard back in place, and - the time-consuming bit - positioned their office fridge so no-one could see it.

Haha, that was my guess. This is like constructing a safe with a super heavy reinforced steel door on the front and construction paper on the sides and top! He could’ve kicked his way through 5/8” (prolly 16mm to you lot) drywall ;) Your solution was a lot cleaner and you earned that tasty reward!