Oh the whitewash

[OwlHoot]

And then a bloke came and adjusted the padlock. Besides, if you can close it from the inside, you can open it from the inside, ...

Not necessarily if you're bundled up like a turkey, with constrained arms, and you accidently drop the key out of reach (which I speculated on in my earlier post)

and is the holdall really strong enough to make it impossible to break the seams from the inside, using the full force of one's legs? ...

If tightly constrained you can't necessarily use your biggest muscles to full effect or at all. I mean for example suppose you were slid into a cardboard tube with your arms at your side, and (in this example) unable to twist them backwards or forwards round your body. How much outward force could you exert with your arms? Not much, I'd suggest.

I still find it a bit far fetched that there was nobody else involved.

Yes, that does seem likely, but wouldn't they have been recorded on CCTV? (The "Mediterranean couple" reported on at the time were later traced and it turned out they had been attending a party in the building. So presumably they weren't involved.)