I'd have to see the flower, but it doesn't look like wild mustard to me. It looks to be in the datura family. Let's send a shout-out to Iochroma for his help on the matter.
I've no idea but check the names you've been given against the pics on www.thetortoisetable.org.uk to see if you find a match.
They will tell you if it's tort safe or not.