Dear Sibylle,
That sounds a very frightening indeed, I trust you are OK ?
You say there is plenty of fluid so I know it's power steering, but is the
power steering belt in tact, it sounds just what might happen if the belt
breaks.
It would be difficult almost impossible to turn the steering on a large car
such as
a Jaguar or Granada or similar.
It could also be something like a universal joint seizing up, between the
steering
column and the steering rack.
Either way, because it's your steering, you should get it checked urgently
at your
favourite garage, you really can't take chances with steering or brakes.
I hope this has helped, good luck great to hear from you.
Regards
Bill@okdiy.co.uk