We had a surveyor round the other day - from the Valuation Office Agency to re-assess the offices & stores. We had queried the description of use.
She spent 1/2 hour measuring up and asking questions.
Only to tell us that the use hasn't changed but the space has grown considering no walls have been moved in over 20 years (think her magic measure was broken ) and from next year we will have to pay more.
I hate to be a sceptic but I think these people doing the deal (and charging you £480 ) are trying to make a fast buck, because as a rule if you querie anything on your business rates, they will send one of their own around to re-assess.
I would check the councils details of what your rates are based on e.g. space & description of use and make sure they are right yourself. If they are different (in your favour) then contact the council dept. and get them to re-do.
Hope this helps a bit.
If not shoot me :D