John,
Town hall was closed for public holiday and so was foreigners office. (In any case the foreigners office said they could not assist.)
From the details I have now received from Paul (See the website below) it looks as though it is the Cadestral values that are much too high.
I think it will be necessary to ask the Patronato office to examine the values and I feel I will need at least 5/6 values for the later part of the development before I can proceed.
Would appreciate if anyone in blocks 1 & 2 ( or others in phase 1) who has an IBI bill over € 460 can send details by private message of their Cadestral values