Hi Nelmo,
Thanks for that, at this stage i'm willing to give anything a try, Lexus have quoted me £800 for a new ignition lock.
They think it could be an issue with a tumbler not engaging or something when the key is withdrawn, my first step is going to be to get the remote fob battery changed, I had it tested about a month ago after a strange issue with the car not starting, then it started but the remote didn't work, so I sat in the car and locked/unlocked the doors 4-5 times, and it worked again...strange cars these Lexus! but i'll definitely look at the battery too.
Cheers