Where you terminate the agency agreement (other than where it has done so for the agent's breach), you will be required to make mandatory payments to the agent by way of compensation for the loss of its business. This is called a "compensation" or "indemnity" payment and which one applies will depend on what the parties did (or did not) elect in their contract and/or what the applicable law is.
In your circumstance, there is no contract, then the compensation alternative will apply by default. This is not a difference without a distinction: while both payments are intended to compensate you agent for the goodwill he has generated for you – the fruits of which you will continue to enjoy in the future, but which the agent will not – they are calculated very differently.
The indemnity is payable if and to the extent that the agent has introduced new customers (or significantly increased business from existing customers) and it is calculated by reference to the agent's average commissions over the previous 5 years, capped at 1 year.
Compensation is calculated by reference to the loss of the value of the agency. The value of the agency is the amount that a hypothetical purchaser would be willing to pay for it at the date of termination.
Usually, a Valuation Expert would be appointed to value the business for the purposes of determining the appropriate level of compensation to be paid. Generally, if the business is a successful one, then the compensation alternative will usually work out to be more expensive for a principal than the indemnity alternative.