Let’s have a look from a further-out perspective.
You DO mind your own business, and a few weeks down the line you hear of a driver from that yard having run over a mum with pushchair somewhere, with the driver being arrested and detained on charges of “drink driving” as well as “causing death”… How are you going to feel, knowing that you could have piped up, but didn’t because you thought it was dishonourable to grass up what seemed to be a yard not taking due care to EVERYONE’s well being, including the wider public? In my mind, the HSE fines issued to yards when a member of the public or workforce gets killed following a systemic unsafe act - is peanuts to all but the very smallest yards. Do these small yards even pay the fines? - Or just go bust, and the entire management gets off Scot free, and opens up a new firm under a different name at the same yard a few months hence? We must have all seen such places if any of us have been doing this job for decades…
In my mind all this apparent “drivers getting trigger happy” at this yard in question though - might be on instructions from the managers to “cover themselves” rather than the drivers. After all, the reported accused observations were seeming to be made up, but got you to doubt your own sanity, and check all over again anyways.
In an environment like this, where it looks like there is a seriously bad atmosphere - It would surely make it easier to take a “hardened stance” and report for purposes of “prevention” what you have found?
…Not that the police or VOSA are actually going to follow it up! You’ve done your bit though, and if someone gets killed AFTER you’ve done your public duty and reported the unsafe situation ongoing at this yard - then your conscience is clear.
I once reported a yard for running their drivers 5x13-15 hour shifts per week, explaining to them that I’d been sent there on agency originally, but refused to turn up for the thursday 4th shift - because the previous three had all been 14-15 hours in length (exactly the same job & long run every night), the tuesday finishing shift barely having me pop my card in time for the 15 hour mark! I also got a bollocking from this yard for filling up at the “wrong fuel forecourt” (company fuel card in cab) and I was also criticized for refusing to answer the mobile phone in the cab. This was a bog-standard phone, not a hands-free kit - so as far as I was concerned, if I don’t have a convenient layby to pull over in straight away to answer it - I ain’t gonna answer it!
Despite having reported them though, there seemed to have been no follow-up from VOSA, since a few months later I heard that rather than a yard being spot-checked and heavily fined by having drivers all over their hours each and every week in some format or other - the bloody outfit had won an award in one of the trucker mags! WTF I thought! The runs in my own experience were giving me the very worst nodding dog experiences each and every of the three shifts I did there though, with me practically needing matchsticks to keep my eyes open when I’m on the last leg back past heathrow airport M25 in the rush hour. This job was quite a commute as well, and after this episode - I refused at all agencies thereafter to commute more than one hour out to any yard where I was given work.
When you think that fairly recently big-shot firm Stobarts got spot-checked and actually had one of their O licences suspended for such offences - perhaps VOSA have since tightened things up a bit, what with this all happening in my experience some years back and all. I wonder of course if the firm is still having all it’s drivers running bent by the thursday of each week though… 
It ain’t a safe environment having to do a maxed-out shift every day, even if that in fact only happens to the agency bod because the full timer has got the job to such a fine art that they can get their hours below 13 for the two shifts per week they need to do to make it all legal. The jobs some people will submit to as full timers! - I dunno! 
