Blimey Ian, I've got a fishing licence and it might be worth the risk of getting caught just to see you in M&S
I contacted the Environment Agency in the late 90s about the state of the river as there was a press report that it had been upgraded from a stream or whatever to a main waterway - the person reporting back to me claimed they knew nothing about that!
It's actually 12 when you need a licence but still illegal to fish under 12 if you don't have permission. The fishing rights generally belong to whoever owns the land adjacent to the river, so DDC own the rights to all the areas where the river is accessible from public paths and roads and don't allow any fishing, full stop. It might be worth finding out if DDC or PCSOs have any rights of prosecution, doubt it though.
Details of fishing licences here -
http://www.environment-agency.gov.uk/homeandleisure/recreation/fishing/31497.aspx
Details of how to report illegal fishing here, basically phone 0800 80 70 60, maybe if we all had a day of action and they had a few hundred phone calls they might take notice -
http://www.environment-agency.gov.uk/contactus/36345.aspx