Aha!! didn`t think of that (duhhhh) silly me.
Oh well, never mind I`ll know better next time but if it is ya PAS belt it`s about 10 mins work with a couple-o-spanners!! and will cost you about.... erm..... ummm... oh teah, that`s right, NOWT!!!
Check that power steering fluid pot though, if it's down it's the rack. I got a second hand one and the whole thing cost £250 incl fitting which i thought was reasonable when u see what vauxhall dealers want for the rack on its own.
Now i know this might sound strange.I had the exact same problem with mine and it was`nt the Pas belt...not saying its not on yours.
It only screached when locking over left hand down from standstill.I replaced the belt and tensioned it correctly but the belt still made this noise.To cut a long story short it turned out to be one off the ABS/TC sensors touching the segmented hub when on full lock.The origional sensor brackets had started to corrode from behind,pushing the sensor closer to the hub.They were replaced with new plastic ones and hey presto?the belt stoped slipping!!EXPLAIN THAT ONE,cos i cant!!(and yes it was definately the belt making the noise and not the sensor touching the hub)
Well my gte makes this noise when going full lock to the left, i think its just strain on the pump making the belt slip, or the pump itself. Its done it for 2 years, hasnt got worse hasnt got better. Vauxmaster's cav does it, my mates old corsa gsi does it. Have it looked at if it bothers you, otherwise turn the sounds up a bit more.