OK,
BS7671 does not define timescales, it suggests them.
Your insurance company will have their requirements which you will need to comply with, to comply with your contract of insurance.
A shorter period than specified is not an issue, you are just doing more than is required by your insurance company/law, which is not an issue, you are doing more than the minimum required.
There is NO DEFINED TIMESCALE IN LAW.
Just like any H&S requirements doing better than the minimum required is not a bad thing.
BS7671 is regarded as the minimum standard, NOT best practice.
There would be no issue in doing an inspection every 3 years rather than every 5 years.
If any insurance company says different then they are idiots, & they would be made idiots of, in any court in the land.
If your installation is correctly maintained under a full and sufficient PPM system, with full documentation of repairs and modifications including certification under BS7671 as required, then it is acceptable under BS7671 not to undertake PIR/EICR checks.
You will not find the timescale for checks in BS7671 it is in the IET Guidance Note 3.
Now as far as faulty installations go, you are then into compliance with EAWR & PUWER, MHSWR etc.
If, the installation is that dangerous that it needs isolation, then you have a SERIOUS problem, that you need to address both in the short & long term, not discover and correct at the inspection timescales recommended by BS7671 & associated guidance.
BS7671 & associated guidance state that from the initial installation, the time to the first inspection is determined by the designer of the initial installation and is defined on the original Electrical Installation Certificate.
There is a very good chance that this could be taken by a court of law to be binding as the designer must be in full knowledge of the requirements of the installation and its use for the design and installation to be compliant with BS7671, thus they are able to define the expected time between completion and first inspection, as the competent person in law.
Following this, the next PIR would indicate on the EICR the time period that the “COMPETENT” inspector & tester of the installation would recommend to the next inspection.
Remembering the requirements of any person undertaking I&T on an electrical installation must have above average knowledge of the type of installation, the environment of the installation, the usage etc. etc.
Therefore as the person undertaking this work must be competent as defined by EAWR, this timescale could also probably be taken by a court to be binding, even if it is less than the timescale recommended in guidance from BS7671 the IET.
What H&S people REALLY NEED to do is to ensure that their companies engage fully competent “entities” to undertake the I&T, and not expect to pay peanuts for the work.
Not , for example domestic installers who have done no training except a 5 week course to inspect & test complex industrial installations because they are cheap, unless they are fully knowledgeable about the installation methods, systems, equipment, and the editions of BS7671 that were in place at the time of the original design and construction.
Preferably, they should be in possession of previous editions of the relevant documentation so that they can make a fully informed judgement on the condition of the installation, not only against the current requirements of BS7671, but, where deviations occur, they can be sure that the installation was compliant when originally installed.
I&T of electrical installations, especially industrial and commercial is a little more complex than it first may seem.
There are too many so called “electricians” out there who are incompetent to undertake even the simplest I&T on any install these days it is unreal.
If you want any more information on what is right/wrong/required/not required, please ask, by PM if required.