Thanks Dougy83.
I have some RFID readers and tags (MicroChip type used in animal 'chipping') and I also have several 40 mm square readers, which seem to work very well.
I also have a couple of the readers and 10 tags that you suggest in your ebay links, but have not found them particularly reliable probably due the the distance from the reader to the tag (which is around 20 mm), and really wanted to come up with something that was very cost effective and small.
I have just ordered a 'AMS TSL250R-LF PHOTODIODE' that converts 'light' into voltage, and by using red,green or amber leds as color enhancers, may be able to detect 'coloured' bars ... I have read something about it somewhere on the 'net so thought I'd give it a try.
I think I may have come up with a possible alternative to pure Bar code reading, but still 'thinking it through' and want to experiment with it before I am convinced it would be worth pursuing.
I'll keep the thread updated with my findings as I progress (or not !!!!)