Gents/Ladies, my diesel Peugeot 205 makes a

Gents/Ladies, my diesel Peugeot 205 makes a grinding sound on full lock (both ways), & I would like to know what is causing this. I shall try as best as possible to list the symptoms. Firstly, the car has PAS & has done 75000 miles. Apart from the noise it is in fairly good condition & there is no undue or odd wear on the tyres & the car behaves as it should through bends & over bumps - no wander or obvious clunks. The noise only appears when full lock is applied & it is possible to keep turning the steering wheel even though full lock has been reached! Vibration can be felt at this point. A rudimentary examination of the roadwheels revealed no undue fore/aft movement & turning them by hand was noise free. Jacking up the car & turning the steering throughout its full travel saw no improvement either. My main questions to you Gents/Ladies, are: Why doesn't the steering 'stop' at full lock? Could it be play in the track rod ends & steering rack? Or could it be worn outer CV joints causing the racket? Or both? Or something I haven't thought of? The power steering fluid is topped up & the car got a new MOT last month. No gaiters are split & there is no evidence of grease/fluid loss. I don't really want to drive the car until I know whether this could be dangerous. Thanks, Boo.
PS, it's a 205 on a K plate not 405.