We recently received a letter regarding business rates with the basis of calcualtion spelled out. We have I am sure received similar letters previously and filed them appropriately as no action is required. It happened that one of the measurements caught my eye and I was curious about the details and where they had come from. We armed a junior with a tape measure and set him to work, placed the results on the appropriate web site and thought nothing further. We had a surprise inspection by a lady with digital camera and electronic measuring device who confirmed our measurements and the use each room was put to. Some weeks later a cheque for several thousand pounds arrived for overpayment going back years plus interest.
The moral of the story is read it, measure it and see if you are owed anything. In our case the critical point was the use rooms are put to. Corridors and store rooms are not payable in the same way as office space. You don't need to fall for the scam of the rates review companies. DIY!