Part disposal- Chargeable gains for Companies

When a company has a damaged asset and receives insurance money for the part disposal, the treatment is specified in the notes as-

“if the insurance money is fully used in restoring the asset the tax payer can elect to have the
proceeds deducted from the cost of the asset for a future calculation thereby deferring any gain
when the insurance is received”

Could someone help me understand how the deferment happens when the insurance is received, and when is the chargeability deferred to? Will the insurance receipt be charged at a later point in time?

Thanks in advance!