Hi. My name is*****'m looking at your question now and will post my answer or ask for more information here in a short while.
Unless your nephew has a share of the ownership of the property, the rental income will be taxable on you regardless of what you do with it. Joint owners of property who aren't married to one another or in a civil partnership can split rental income however they wish regardless of the ownership proportions but there has to an ownership interest.
I hope this helps but let me know if you have any further questions.
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I trust you are aware of the non-resident landlord scheme. Take a look here for more information.
Even though you will be non-UK resident, you will be entitled to the personal allowance to use against your rental income.