Think through what you want now and longer term. If you can get away with a "glorified extension cable" for less than 13A it is an easy, cheap and quick route to having electric out there safely.
But if you want it more permanent, or want to have extra capacity, then get an electrician to look at it. You would end up with a dedicated circuit from your main board, but depending on the needs on reliability you might go for a fused-switch from the meter tails feeding the SWA cable instead of another RCBO.
Basically if you have a RCBO/MCB feeding the outdoor stuff you won't easily get selectivity with any down-stream protection. So if you blow a fuse on a 13A outlet it will probably trip the feeding MCB/RCBO as well as any local breakers. That may not matter to you if lights go off, etc, but in other cases it might be an issue (say you have a freezer on a 2nd circuit and you don't notice it has gone off and de-thawing everything).
However, if the feed SWA is of adequate size and so the feed fuse is relatively big (say 30A or more, but it depends on the downstream stuff) it will usually survive long enough for the down-stream fault protection to clear the fault.
Another factor in the cable / system design is if you need any earth bonding for "extraneous conductive parts" in the garage (steel structure, water pipes, etc) and you are on a TN-C-S supply (where your local earth and neutral are common up to the meter cut-out). In those cases you are required to have a minimum of 10mm copper-equivalent earth conductor size due to the potential high sustained fault currents if the PME goes open. Or you do a separate earth rod for a TT style of arrangement.
So plan what you want to do with all these factors in mind.
But if you want it more permanent, or want to have extra capacity, then get an electrician to look at it. You would end up with a dedicated circuit from your main board, but depending on the needs on reliability you might go for a fused-switch from the meter tails feeding the SWA cable instead of another RCBO.
Basically if you have a RCBO/MCB feeding the outdoor stuff you won't easily get selectivity with any down-stream protection. So if you blow a fuse on a 13A outlet it will probably trip the feeding MCB/RCBO as well as any local breakers. That may not matter to you if lights go off, etc, but in other cases it might be an issue (say you have a freezer on a 2nd circuit and you don't notice it has gone off and de-thawing everything).
However, if the feed SWA is of adequate size and so the feed fuse is relatively big (say 30A or more, but it depends on the downstream stuff) it will usually survive long enough for the down-stream fault protection to clear the fault.
Another factor in the cable / system design is if you need any earth bonding for "extraneous conductive parts" in the garage (steel structure, water pipes, etc) and you are on a TN-C-S supply (where your local earth and neutral are common up to the meter cut-out). In those cases you are required to have a minimum of 10mm copper-equivalent earth conductor size due to the potential high sustained fault currents if the PME goes open. Or you do a separate earth rod for a TT style of arrangement.
So plan what you want to do with all these factors in mind.
