Good news I got a new steering rack fitted today (within 24 hours of diagnosis!)
The odd thing is that the car supposedly had the modified rack which was a fix on the historic steering problems pre 2008.
Had an identical problem happen to me yesterday, reversing off the drive and steer became unusable. My problem is although my car isn't quite 3 years old (06 Plate) it has done 62,000......I am going to try and get Lexus to pick the tab up for this today :(