HMRC Admin 10 Response

Hi
The scenario you describe is complex international tax planning and we are unable to give you a response other than to provide you with the link already given.

Hi
Your question suggests errors have been identified within a company tax return that is out of time to amend.  
It also suggests the corporation tax liability has increased and not reduced as otherwise there would be nothing available against which to claim double taxation relief.  
An amended return can be submitted if you are in time to do so.  
If not, please write to
HMRC,
Corporation Tax Services,
BX9 1AX,
setting out the adjustments together with an amended computation with a detailed calculation of double taxation relief including details of any underlying tax relief claims.  
Please note, we may ask for evidence of the foreign tax paid as set out in
UK residents with foreign income or gains: claims for double taxation relief against UK tax: evidence

Hi
I refer you to the UK/Italy Double Taxation Treaty (DTT) available at:
UK/ITALY DOUBLE TAXATION CONVENTION
A company is resident in the UK due to its incorporation here or where the central management and control of its business is in the UK.  
If the Italian Tax Authority also consider the company to be resident in the Italy, then the tiebreaker in the DTT between the UK and Italy would need to be considered.
It is unclear from your question whether the you as the sole director intend to be resident in the UK or Italy which is a factor you will need to determine as that will be a consideration in establishing central management and control.  
If the facts and the DTT confirm the company is resident in Italy, the subsequent appointment of directors outside of Italy (or any other changes) could mean that its residency status also changes.
Corporate residency is covered in the link you refer to but there is a much wider guidance starting at :
Company residence

Hi
You need to call our Helpline (0300 200 3410), to confirm that the record has been set up and check if the letter CT41G (which includes the UTR) was issued and when.
The Helpline colleague will be able to re issue the letter, if needed.

Hi
If you are registered in the UK, you are required to declare all income on your return whether UK only or abroad and will be liable for corporation tax for the full period on all of it.
If you are required to pay tax abroad on income made there, you can claim relief under the double taxation provisions.
So essentially there is no apportionment, you will declare the full amounts.