I'm aware of someone who was a driver at Thames Trains who left and became a driver at LU, they used to post on here. Not sure if they did a stint on stations first or were directly recruited. There may be one or two other instances but I would think since privatisation it must be rare. On the other hand I can think of many colleagues who worked for the mainline under BR as guards or second men who left to join LU because the pay for equivalent roles was better, all of whom have now been drivers at LU for many years. I can think of one who was a YTS trainee under BR, was latterly a driver for LU and has now returned to the mainline via the trainee driver route. I'm not sure if they made it to the driving grade under BR prior to joining LU.