There are two types of Excess, the Basic or compulsory Excess, and then there is the Voluntary Excess.
The Basic excess is a value you must pay in the event of a claim. The payment is usually made to the garage that has fixed your car. In most cases with an Insurance company when getting a quote, you can lower or increase your Basic Excess. By lowering the Excess your monthly premium will go up, by increasing the Excess your monthly premium will come down. Over time, if you don’t claim, then choosing a higher Excess may pay off well since you will have saved more compared to if you had to claim and paid out the Excess amount.
This is an amount you can choose to pay in addition to the Basic Excess and by doing so you will likely bring down your monthly premium even further.