it is probably oil seed rape. they do put that and mustards in the seed mix. if you have farms/fields near by that could be the place it originated from.

welcome to GoY too ;o)

Gosh thank you so much - I never thought of that - we have tons of fields of it around but I've never seen it up close. I was thinking more of a wood type plant as we have those around too. It is a beauty for sure.

don't let it self seed or you will have hundreds of them. collect the seeds just before ripe dry them in a paper bag and then add the seed to your bird mix.

Oh okay, I guess it's probably a tad over the top for a small garden - shame though - at least my birds will benefit!