NRL: should letting agent fees be deducted before or after tax?

I own a property in the UK but I live in Ireland and have my UK tax deducted by my letting agent. I recently changed letting agent, and my new agent deducts tax AFTER applying their fee to the gross rental income. This benefits me, but I am worried that it is incorrect and they should deduct tax from the gross income BEFORE applying their fee (or any other fees). Which method is correct?

Hi,
You can claim for professional fees paid to an agent. These get declared at box 27 of the property income page and are deducted from the gross property income.  
The tax due is then calculated from the net profits once expenses have been deducted.    
There is a help sheet available on our website gov.uk, which can be found by searching for UK Property Notes.  
Alternatively, you can contact the NRL department.  
Their contact information is found here:
Non-UK resident landlords 
Thank you.