Can’t help with your specific case I’m afraid,but a couple of trade platers with brand new Volvo tri-axle coaches(for delivery to Ireland) were parked up today with hazards on.I stopped,thinking they were lost.Turns out they’d seen signs that the Britannia bridge was closed to high siders.They phoned N.Wales police and were…eventually…told that a hsv means anything bigger than a car,so they were NOT to go over the bridge.Strange thing is-I’d just followed several artics coming off the boat over the very same bridge 
Sir +:
Can’t help with your specific case I’m afraid,but a couple of trade platers with brand new Volvo tri-axle coaches(for delivery to Ireland) were parked up today with hazards on.I stopped,thinking they were lost.Turns out they’d seen signs that the Britannia bridge was closed to high siders.They phoned N.Wales police and were…eventually…told that a hsv means anything bigger than a car,so they were NOT to go over the bridge.Strange thing is-I’d just followed several artics coming off the boat over the very same bridge
I came off the Stena boat at lunchtime and I just went over the Britannia Bridge, as did all the other trucks running with me who had come off the ferry including a double-decker right behind me. I went over at 20mph and it was fine, I was pulling an empty, 4.0 metre, box trailer. One of ours heading to the ferry did divert and it took him about 45 minutes to queue and get over the Menai Bridge as the trucks were crawling through with it being so narrow.
Deathstar:
The chances of a vehicle being blown over increase when the walls join the roof at right angles,i.e.90 degrees,Those where the join is made via a convex curve have better aerodynamics and take more effort to blow over.I remember seeing it demonstrated on TV once upon a time.
Can remember my cousin saying that a few years back.
One of his drivers was getting “a bit twitchy” about taking a Furniture van out in high winds to be told
“its got a curved roof, they dont blow over” . . . . It did,just as he got over the Thelwall.
Driver was wearing a seatbelt- saved his bacon.