h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I am in the process of buying an old property and I have some worries about the septic tank system. First some facts: the property has been vacant for around a year with all plumbing/water systems drained down; I am told that the septic tank has not been pumped out for 10 years!! I do not know how old the septic tank system is or where the soak-away is located. I am concerned that after 10 years (without any cleaning), solids or scum may have entered the soak-away and blocked it. Moreover, as the system has not been used for a year, this may be difficult to determine until I flush the WC for the first time! Whilst a specialist company could examine the condition/age/size of the tank for me, will they also be able to determine the condition of the soak-away and whether it meets legal requirements? Thoughts gratefully received.
Rob