Jules, I'm afraid I agree with the advice you received that your PC should be registered with the ICO. In addition to to the sound and visual images, do you not hold other personal information such as names, email addresses etc of Councillors, contractors and parishioners?
Transparency is a key requirement under the Act. People have a right to know in advance how their information will be used. If consent is not given on a fully informed basis, it is generally invalid. So, in our case, if we say we are recording the meeting for the purpose of the minutes, we won't have consent to use the recording for any other purpose.
I am aware that there was a case last year of a company which had CCTV in its staff room. The signs said this was for security purposes (items had previously been stolen from the fridge). A staff member was (correctly) accused of writing offensive graffiti in the room and the internal disciplinary committee viewed the CCTV as part of his disciplinary procedure. The staff member took them to the High Court for doing do, and the court agreed that the disciplinary committee was not viewing the recording for security purposes, but for disciplinary purposes, and had breached the Act. I am assuming the same would apply here.