Having paid my first half in bank whilst in sicily,

If I make a payment from my UK bank I put the ref... I would have thought most UK banks are the same and allow the addition of a reference? Guess it would depend on the size of the reference field, but your CAP (post code), Contrada house number would be enough along with your name which will be on your account. Are you sure they don't also need a confirmation of payment e.g. the Poste here when paying online give an authenticated payment receipt with its unique reference number.... After all paying here over the counter you have to have 3 copies of the F24 stamped...

I paid the first half earlier this year from the UK.  I had to put certain information in the 'comments' box of the internet transfer to both payments [Comune and State] and also had to send confirmation by email [attaching scans of the 2 confirmatory slips sent to me by my bank] to the Comune.  The December payments have the similar information requirements in the 'comments' box, but the words change to show it is the second payment. I know my explanation isn't that clear, but go to your comune's website and 'search' for IMU - there should be an information sheet with all the requirements on [at least several comunes websites I checked on last time did - I had to check them out 'cos my comune had posted the wrong IBAN number for the State payment!!]

Anyone from the Licciana Nardi area!! Just done my calculation for Dec  total for the year 1700 euros half to pay now. Thats up from 600euros we used to pay for the year. Have checked and seems to be the going rate,

Not from your area; however, there has been big increases this year. The difference you have to pay sounds right. Next year there may be some changes as it is supposed that taxes are going ti be calculated on habitable area.

found the following web page which looks about right. http://www.italy4me.com/index.php/living-in-italy/finance-and-tax/114-how-to-pay-imu-from-outside-italy

If you didnt pay in June, or your comune has fixed an aliquota different to the default, you must pay the difference plus (if late) the sanction and interest, putting  a cross in the AVV box if you're using an F24.