OK PauL and Henry now I am frustrated. It works for you, but when I follow Pauls instructions I get to the bit where it asks me to select a line, I select the line, it does nothing except ask me to select the line again and again and again. I have the work plain set to the face and the line is definitely on the face it selects OK but then nothing.
I had one last go before submitting this and guess what I turned off the construction so that the line pick was direct rather than through the little selection window where I had to decided between the construction line or the solid line and it WORKED!!!