The UK Valuations Office has slipped out a corker during the quiet summer period with the Olympics on.
From January 2015 (yes, retrospective) occupants of any building that does not have direct access between floors will be separately rated rather than treated as one joint rental. This leads to a much larger tax bill. Even if you rent and office and use the common parts, stairs/lifts etc, it won't count.
And this is retrospective. Helpfully, businesses wont knowhow much they owe until the VAO gets around to telling them.
Honestly, what a shoddy way to approach tax collection. It is highly aggressive in the extreme.