To a great extent I agree with Colin that the number of Fire brigades who do this is probably minimal, however it is not only the fire legisaltion that is involved it is also the HSAWA any incident involving electricity particularly if someone got hurt would immediately bring in the HSE and we know how they love to get into the Fire Brigade.
Secondly with regard to shutting down Control all Brigades should have a procedure for maintaining Mobilisation if the Control becomes untenable, in the old days this would be a package curtousy of the IRA, nowdays it could be anything. Moving to a back up control should be regularly practiced so that everything goes smoothly. So to carry out the 5 yearly fixed inspection Control will just move.
The other aspect is that although it is a five year test there is no requirement to carry it all out at the same time. Most large buildings carry it out on a phased basis 20% of the installation each year giving a 5 year cycle.