I did a little research during the week, and ended up speaking to the leasehold advisory service (http://www.lease-advice.org/). They said exactly the same thing, which is why I am now going to pay up (with a letter stating it's in protest) and then I'll be looking into whether to contact the LVT about it or not.
Until yesterday, my only contact with Becki Smith had been by letter. But I called her number yesterday regarding the roller shutter door. She pointed the finger at Bellway, so I called them, they pointed the finger at her/Scanlans. Neither of them were willing to do anything about it, and had no regards for our security or the fact that our home insurance and car insurance would certainly never cover us should anything happen whilst the door was locked wide open. They just said it was the only way that they could ensure that all the keyfobs would be collected.
A little more consultation would have been nice, rather than a letter on the day they locked it open!
At least we can shut the door again now