Fair terms and conditions for cancelling contract with Letting Agent

Tenancy Types and Management

Hi Everyone

I am currently reviewing contracts with letting agents and am trying to establish what a fair condition would be if as a landlord i do the following

I instruct the letting agent for a full management service. Lets just say for arguments sake they charge a 10% + VAT charge for the management service.

What would you consider a fair charge for the agent in the case I the landlord want to end my contract with them .

1. with the existing tenants in place

my current agent requires 3 months notice plus 1 month rent +VAT charge. Is this fair? What are other landlords agreeing to?

1. would it be any different if the existing tenants were in the property for 1 , 2 or more years. Is there a case no charge should be applied (only a notice4 period of lets say 4 months) if tenants have been in place 2 or more years?

Thankyou

Raji