A Virgin Atlantic flight that was supposed to leave the UK never took off after passengers spotted a potential safety hazard ... which makes up the nuts and bolts of this story.

Here's the deal ... last week, this VA plane that was due to depart from Manchester to New York -- but before it could even get on the runway, eagle-eyed guests onboard noticed something was amiss on one of the wings outside, and they flagged it to the staff.

Basically, they thought they saw some screws missing -- and as it turns out, there were, in fact, four missing fasteners that needed to be attended to by a maintenance worker.

That's the video you're seeing here ... the guy is literally drilling in the fasteners/bolts that had apparently fallen off -- and as you can imagine, everyone onboard was shocked by this apparent oversight. Now, in terms of the safety of all this ... VA insists nobody was at risk.

An Airbus rep clarified to TMZ Monday that the missing fasteners/bolts were actually part of a panel on the plane that only affected the aerodynamic levels of that specific piece -- and did NOT have any impact on the integrity of the aircraft at large.

Virgin Atlantic tells us, "The VS127 from Manchester to New York JFK on 15 January, operating on an Airbus A330, was canceled to provide time for precautionary additional engineering maintenance checks, which allowed our team the maximum time to complete their inspections. The safety of our customers and crew is always our top priority and this was not compromised at any point."

The Airbus company that actually handles the plane itself tells us there are actually 119 fasteners on this part of the plane -- and notes the 4 missing ones wouldn't have made the flight any more dangerous .

.. with that said, they made sure it underwent additional maintenance just to be safe -- and they also note the fasteners were replaced.

All the passengers ended up having to deplane and figure out other travel arrangements.