Does it open on its own? Is the switch set to max?

Yes it does open with key fob and door switch and it's on max.
Should it be on 3/4?

Thanks for taking an interest
John

There was a recall for ST's with the powered strut. Should be (if that's the problem) fixed under warranty. The recall goes back at least 2 years

Yes max opens it up fully and 3/4 opens it but not as far incase your in a low carpark

If this is your issue I'd address immediately.

Thanks
Vauxhall did replace the left strut under warranty, but still doesn't help??
Im loathed to give the the car to search around for a fault with their hourly rate!!
Any ideas?

As you look from the rear the right strut is the powered one. This may be leaking internally, with seals perished? If it opens normally and then begins to fall, then I think its a leak.

But it was only replaced a month ago???
I can't see this been a problem and there's no sign of leakage?

Any other ideas plz?

I had same issue just few days ago.
Opens ,but won't stay open, it just drops down and shoots.
The new LHS strut cost about 80e.
the new RHS strut something around 120e.

I decided to go for second hand LHS strut, didint want to waste 80e or 120e at that stage , cause didint kwow if the new ones will work.

I got it for 20e. Replaced my self and it's workt. Perhaps I was lucky.

That's my story.

I'm afraid I can't offer a solution as such, but in case you've had the problem since owning the car and never known it working properly, then it might be useful for you to know that when the tailgate is lowered using the switch/keyfob you can hear the motor actively controlling the descent of the tailgate in a controlled and steady speed with the lock then auto engaging when it reaches the bottom.
I may be wrong but I would of thought if the problem was a sensor or electrical then you would hear the motor operating as it sensed some sort of issue. If the tailgate is lowering pretty silently without an associated motor noise then would possibly hint towards a leak in the struts. The tailgate is damn heavy (I had to open it without motor assistance once and it took some effort!) and would require the motor to lower in a controlled way.
Apologies if you've already considered this but thought a bit of comment from an owner with a correctly operating tailgate might help. oh, as for the beeping noise I only seem to get it every now and again when opening and closing the tailgate though the hazards do flash when operating. I did test drive another ST before mine (though a couple of years older) and that did beep more than mine. Mines a 61 plate ST elite by the way.

It's not unheard of for new parts to be faulty.
Was tailgate working correctly after Vauxhall replaced strut? If it was I would go back and get them to check new strut.