Cris I thought it was rape but the thing is the farm hasn't grown rape for some 15-20 years. It is something he's sown to help the soil. Next time I see him I'll ask what it is. Maybe it was an autumn rape?
A farmer I know says the big problem with phacelia is not growing it but stopping it growing in subsequent years. I suspect this is both due to seeds set after early flowers and also due to seeds not germinating the first season and lying dormant. It is simliar for oil seed rape. The fields around here are ringed by yellow flowers long after the OSR has faded. I put this down to plants originating from OSR seed years earlier and which have now become established and are reverting back through successive generations towards the original plant.