It'has been out for a couple of weeks now and beginning to peak. Wild Mignonette or Reseda lutea grows in any marginal or ruderal areas, especially in the south east and especially on chalk. Hence it's common round these parts.
It is a native but Geoffrey makes no mention of it. It's big sister, Weld, gets all the plaudits. I shall try to find some and blog it later.
This was growing by the path as I walked back to my car after work and I couldn't resist a few snaps.