Sevice wheelnut tightening

Where have I said the bolts snap?

I have said no such thing nor have I said here in our case the bolts are taken into yield. 

What I am saying is the wheel will be on its way off, long before the bolt and its tell tale ever rotate. Any rotation happens at the very end long after the wheel is shuffling about unretained just held loosely on the bolts.

Vital in wheel retention is retaining adequate tension in the bolt, that can be lost, and typically is, without the bolt turning at all.

When I pick my caravan up after servicing they always re torque the wheel nuts while I watch but  never ease off the wheel nut1st. If this is incorrect do I report this to the ncc.

The user and all related content has been Deleted User

I think he might argue that point.  I can’t argue if he is right or wrong because what I have read on here might be wrong. Every caravan service I have had the person torquing the wheel nuts has never slackened them off 1st. I have had my vans serviced at various ncc workshops just for warranty purposes. Maybe the ncc should send out instructions of how do do this task proper especially if from what I read on here it is wrong.

The user and all related content has been Deleted User

but when checking wheel bolts/nuts, you're checking them for being slack and assume that when they were originally fitted they were torqued up correctly. If when checking them 20 miles up the road after a tyre change etc you slackened them first you'd end up in ever decreasing circles of slackening & tightening bolts/nuts every 20 miles.

I get the slackening bit when the wheel was originally fitted. I tried to reason this point at a high street tyre place after he'd fitted a wheel to my car using a windy rattle gun. The torque wrench did not move the bolt at all ...... it went completely over his head. 

and being required to watch the fitter tighten the bolts is also assuming that the torque wrench used works. Unless it'd just come out of the box or just been calibrated how would you know?

The user and all related content has been Deleted User

As a blanket statement without history that's rubbish.

If a bolt has been torqued correctly it will have been 'stretched' to within safe limits along its length, and will return to its original length when loosened, allowing re-use.

However without knowing its history the bolt may have been overtightened, in which case its elasticity has already been ruined and no correct torquing will bring that bolt back to its original shape.

If you are not certain then replace the bolts, as loosening and re torquing means nothing without knowing what went on before. 

And if he had first slackened over torqued up bolts with it without resetting way above the required value he would most probably negated the calibration.
If on the road you just check the bolts have not relaxed enough for the torque wrench to advance them, you will have IMO done all that is sensibly necessary.
Bolts in this application that are not renewed each tightening, as the plating condition has an important influence on their friction so the tension developed, don't have the degree of precision others are implying. It is therefore all a bit academic if they need loosening or not, just rechecking they are that tight is all that IMO is necessary, and without carrying a breaker bar as well as a [break] torque wrench all that is sensible to do at the roadside.

I have never seen an Al-Ko published technique statement that the re-torque requires loosening. Where have others found this mandated?