Yes skyhigh I thought about the correlation about booze and coughing but I was still cough free after 10 months on the limited wagon. On nightstops I do go down the nearest pub but it makes no difference to the coughing and hacking. In fact I barfed up a lung in one session and the barman thought it'd gone down the wrong way. Same once with a landing clearance response I was giving and the F/O (PF) thought it was a sandwich I was just finishing up chewing. He nearly dinged the cabin crew button.
Tried gargling everything from Plax to Scotch to coconut oil but no joy. So it doesn't seem like bug or booze related.
I'll try to take honey as you suggested.