Another mucolytic to try is Erdosteine. I've been on Carbocisteine for around 10 days now - if I don't get a result in another 10 days I think I'll try Erdosteine.
Ginge - you've been really helpful, old chap - much appreciated. I am concerned that my GP has run out of patience and intends to leave me in the hands of specialists now - I get the impression his suggestion of Acid Reflux was a last-ditch attempt to help (although he could well have a point - I live on very hot food and invariably eat late at night...). If you can find a minute, would you be able to post a link regarding which foods are good / bad? I've been using Google, but there's so much conflicting info out there regarding foods...the amount of quack websites is shocking
BTW - Bricks placed under bed - thanks!