Hi,
Thank you for your question. Based on your own circumstances, I would advise that on your Tax Return, you should declare the full amount of rental income in regard to your rental business, then any fees etc paid to the Letting Agent can be claimed in Box 8 if you have a Furnished Holiday Let, or Box 28 for a regular residential property.
In order to assist in helping to work out your rental income figures and allowances, I have attached guidance from Gov.uk outlining allowable expenses and which boxes they may be claimed:
Property allowance
Thank you.