Today I was stopped after buying a DVD player by a store worker who told me I would have to supply my name and address for TV licencing purposes. 
I advised her that it was a dvd player and you don't need a tv licence for that, and she called over the security guard, who was standing in the background the whole time. She then tells me it is store policy.
I told her again that there is no legal requirement for my details to be taken and that even if they were I did not give my consent for them to be held or passed to a third party as this is against the DPA.
At this point I was just going to walk out, but I didn't want to cause a scene.
Am I right in thinking that:
a) If I had walked off and they had tried to detain me, not only would that have been assault, but also false imprisonment?
b) When does store policy over ride personal liberty and forces the employee to commit a criminal and/or civil offence?
If I had just walked out the security guard would not have been able to stop me, but this officious little witch had to make sure with a supervisor that it didn't break store policy.
What are your thoughts?

I advised her that it was a dvd player and you don't need a tv licence for that, and she called over the security guard, who was standing in the background the whole time. She then tells me it is store policy.
I told her again that there is no legal requirement for my details to be taken and that even if they were I did not give my consent for them to be held or passed to a third party as this is against the DPA.
At this point I was just going to walk out, but I didn't want to cause a scene.
Am I right in thinking that:
a) If I had walked off and they had tried to detain me, not only would that have been assault, but also false imprisonment?
b) When does store policy over ride personal liberty and forces the employee to commit a criminal and/or civil offence?
If I had just walked out the security guard would not have been able to stop me, but this officious little witch had to make sure with a supervisor that it didn't break store policy.
What are your thoughts?