Chiarimenti: If one is tax resident in Italy (based) and is paid 'lordo' abroad, one should declare this income in Italy (and pay taxes, if any).
Il problema: For the year after this Il Fisco (normally) wants the same amount of tax paid for the following year, paid IN ADVANCE. If one overpays, one waits for the refund (about 3 years). If one underpays, gets a nice multa and pays the difference.
Possible solution: Pay the tax in the UK, but can't claim back for expences like mortgage interest (up to a limit) etc.
Note: The total of NI and Income tax for my salary (capt) works out about the same percentage (30 to 33%).
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