East Lothian,
United Kingdom 
These are better pictures of the yellow crucifer. I am sure it is the same family as wallflowers. The stem is sturdy and woody, almost square. I am sure I have seen a deep purply blue variety of this plant.
Thank you for information about small tree.
SG
16 Jul, 2011
Answers
Me again, it was Drc who suggested it - and google says there are lots of yellow varieties. 'Yellow Bird' is popular and a possiblilty, but it's not the only candidate.
16 Jul, 2011
I think it is probably yellow bird so thanks to you both. I think I have also found the purply blue variety.
Best wishes
SG
17 Jul, 2011
Looks like a nice yellow wallflower - I forget who suggested Erysimum, but I think they're right.
16 Jul, 2011