I'm not sure whether "questioned" just means when you are at the police station or also during the time of the arrest. I would assume it could refer to both "why did you not bring this to the attention of the officer at the time of the arrest?".
Although I would imagine a rational jury would think that waiting for legal advice was a sensible thing to do.
Regards duty solicitors, I always thought that these were really private solicitors who were put on a rotation and were strictly kept separate from the police?
http://www.jfhlaw.co.uk/faqs/crime-faqs/what-is-a-duty-solic...
If there is a case of corruption here then that would be extremely worrying as the people most likely to be charged with crimes are also the people with the least ability to pay a private solicitor. Is there anything to back this up?
I'm also not sure I would want a solicitor who "hates" the police, I would want somebody motivated to help me, not get one over on someone else. The adversarial relationship between the police and solicitor should be professional and not personal.