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Bernie you're not explaining it very well for anyone to try to help.
I think Jon was meaning is the rivnut in the bracket that is fixed to the car that then the A frame pivots off.
Or (most likely) is the rivnut in a part of the car (chassis?) that the bolts screws into AFTER it goes through the bracket as above.
Why can't you get to the 'backside' of the rivnut? Is it inside a box frame part of the chassis?
Have you got all fixtures out of one side?
How did you hurt your arm? Angle grinder kick back?

No angel grinder...I will put another picture up tomorrow...all will be explained... oops I think a red head has that phrase
Bernie.

rewritten to remove ambiguity

Hold the head of the nut/bolt in a ring spanner and drill it out.
Use a bigger drill and cut through the side on the rivnut while you're there.

I'm guessing it is a captured nut welded in the 4 corners when the chassis rail was in two parts before it was welded together, no way to get to it without using a hole saw from the other side of the chassis rail.

If you have manged to get the head off the bolt, find or machine a piece of tube to fit over the bolt stub with a small drill hole through the centre so you can get a centre hole drilled through the bolt. Bigger drill bits in small steps till the bolt is drilled out enough to get the bracket off.
Do you need to bolt something back on using that bolt hole? If you do, it might be easier to cut that part out using a hole saw, weld a new nut on the backside and weld the piece back in. What ever bolts on will cover the repair so no one will know

T1 Terry

No Terry they are rivnuts I have the other side off.
I need this one out so I can put this car back together, all the towing attachments are going on the New car.
Not working on the car today...having a sickie Plus we had guests.
Bernie.
These are the rivnuts on the side I have off.

Cut the head off the offending bolt, if you can't ply the bracket over the remained of the bolt then do the drill thing until you have enough of the bolt gone so you can get the bracket off. If you need to bolt something back on there, grind the flange off the rivnut and punch it through, then fit a new rivnut in the empty hole. It will send the next mechanic crazy trying to find the rattle in the front

T1 Terry

Bernie, watched a friend take out rivnuts, he made a jig that sits on the outside of the metal and surrounded the nut, then screwed a bolt half way into the nut, attached the jig to the bolt and pulled out the nut. It was a bit like a wheel puller but clamped around the bolt head and the base of the jig held the thin metal firm so it didn't buckle. You can buy rivnut removers but this bloke made it himself and it only took a few minutes to make in his workshop.

Crickey....

Put a ring spanner on the bolt head to stop it turning.
Then get a drill and drill out the bolt.

There is even an aligning mark on the bolt head to maintain the center.

What's so hard?

My back at the moment Jon
It will get done.
I don't have to save it just get the plate off so I can put this one back together (the car)
Thanks for the input NP.
Bernie.

yeah, even so, drill it out. Fastest and easiest way to remove the head.