The short answer is: nothing!
If you transfer your judgment or order to the High Court for enforcement by a High Court Enforcement Officer (HCEO) and enforcement is successful, then the debtor pays the associated costs and court fee, as well as the original debt and judgment interest.
Once you have your judgment or order, you use form N293A to transfer it to the High Court for enforcement. There is a £66 court fee for the transfer. If enforcement is successful, then we will recover this court fee for you from the debtor.
Sometimes enforcement is not possible: the debtor may have disappeared, gone bankrupt, or there are just no assets available to sell. In this case, you will pay a compliance fee of £75 plus VAT. You will have also paid your initial court fee to transfer the CCJ. So, even if enforcement is unsuccessful, your outlay will have only been the £66 court fee and the £75 plus VAT abortive fee.
When enforcement is successful, then the HCEO will not only recover the money you are owed, he will also recover your court fee and judgment interest at 8% from the debtor. The costs of enforcement are also paid by the debtor. So the HCEO will seize goods of sufficient value to cover the original debt, the court fee, judgment interest and enforcement costs.