Installing power sockets and light into an adjacent garage

I would like to add two double sockets and a light to the garage. The garage is attached to the side of the house. Currently a spur has been taken off the back of a socket inside the house to provide a single socket in the garage.
I understand the correct way to do this would be to run a separate circuit from the consumer unit to the garage to feed the double sockets. You would then take a fused spur off the same circuit to provide power for the lights?
The only problem with this is the consumer unit is full and an additional extra mini consumer unit has already been added for a shower. Is it time for a new consumer unit? Alternatively would it be feasible to extend the downstairs ring main into the garage instead or would this be classed as a bodge? The area covered would not exceed the maximum area for a ring circuit?
Any help is appreciated.
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