The question of whether or not you are non-UK resident can be complex and you have to consider the provisions of the Statutory Residence Test.
Even if you are a non-UK resident for tax purposes, you will be within the scope of UK tax in respect of any property income from UK properties. You can receive your rental income gross, subject to HMRC agreement and return your income and expenditure on a self-assessment return. Alternatively, your letting agent can deduct tax from the rental payment less any expenses they have paid and remit the net amount to you.
At the end of the tax year the agent or tenant must provide you with a certificate of the net rent paid to you and the amount of tax deducted and paid over to HMRC.
You will then need to send in a tax return showing the income and expenditure. If you have paid too much tax, it will then be refunded to you or you will need to pay any additional tax due.