New garden room electrics

Hi I'm planning on building a new garden room building. Probably 6 × 2.5m or summat like that. Obviously wanting some sockets and lighting in there. I've done a bit of research online and mostly it says to run straight from consumer unit in the household. The problem is I have no space in my consumer unit. I have a outdoor socket on rear garden wall which is fed from a fused connection unit on inside, this fcu in on ring main which is rcd protected in consumer unit. Could I take a spur from the outdoor socket or change it for an outdoor junction box and feed garden room via swa cable? When I say me I mean an electrician...just after the info so I can get things sorted. Its about 8m from house where I plan to build
Thanks
Mark

Depends on how much loading you are expecting from the garden room. Your electrician is the best to advise as he will be on site.

Thanks for reply. I'm just after a couple of double sockets and 6 spots in ceiling void. Maybe 4 spots on overhang of the roof to front and maybe a double external socket for lawn mower ect. Doubt I'd be able to hall a wall heater in there

magico said:

The problem is I have no space in my consumer unit.

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Install another one, or replace the existing.

There is always a way, or many ways, to do this, very few are DIY things. Most of them can only be investigated on site.

If i were doing the job I would first look at the practicality of extending the existing ring final to provide power for the sockets. And extending the lighting circuit to provide power for the lights.
Adding to the FCU spur is not going to give you any flexibility of loads.