You would test the Zs at the spur and make sure it was in spec with the allowed value given by BS 7671-2008 for the protective device installed at the source. At least then you would know if it was going to operate the device within 0.4s for TN or 0.2 for TT should a fault condition arise.
There are multiple factors when carrying out these types of work, type of supply at origin, type of device for the circuit, bonding conductor size and so it goes on.
If you were carrying this job out under the NICEIC guidelines you would also have to complete a minor works certificate which asks you all these questions to keep you on the right side of the law.
Hope this helps or confuses ??