The NICEIC have been making a big thing about working live for some time now.
In Certsure's Magazine Winter 2017-18 issue, there is one technical article on 'Prospective fault current in domestic and similar properties'.
It describes consumer units to BS EN 61439-3, single phase supply 250V, via a service cut containing an HBC fuse to BS 1361 Type II, not exceeding 100A.
It also states the maximum prospective fault current declared by DNO, suitably connected to take account of service cable length, does not exceed 16 kA.
It demonstrates the tests, and reasoning for.
It finishes with a section on EaWR 1989 & live testing, and a section headed Conclusion. In the Conclusion '
and where conditional rating is applicable, it follows that carrying out an unnecessary test to determine the prospective fault current at the origin, or indeed elsewhere in the installation, is unjustified live working and hence could be seen as a breach of Reg 14 EaWR 1989'.
I think I've done a fair precise of the article, the issue (magazine) is not freely available as a download at the moment. Perhaps this is one of the live tests (not to carry out) your colleagues spoke of?
Have to say, when I've had my Elecsa assessments, I've been asked to demonstrate these (live) tests.