Are you talking about the 12v or 240v circuits? For 12v you should have a spare circuit breaker on the panel or you can use the existing 12 v socket circuit. For 240v you wire in your new outlet to the consumer unit on the panel. In my case I have a circuit of two extra sockets, one for the battery charger and a double alongside the chart table. I used UK type domestic sockets so I have a choice of the continental type on the panel or the UK type.
If you are concerned about doing it, employ an electrician.