Hi I have a garage that I want to put an electric shower into. There are also going to be 11 sockets and 11 lights. The sockets are going to be wired in two radial circuits. There will be a 10 square armoured mains cable from the house to the garage. What size breaker should I use in the house fuse board and what size main switch fuse should I use in the garage fuse board

You should put your location in your profile, or at least tell us what country you're in.
We have a few folks from outside the US and Canada so this would be good to know.

Are you UK? Australia/NZ?

If your garage is a detached building, then (here in the U.S.A.) you cannot run 10 circuits to the building.

You would need to calculate the load that the garage will need and then size the four wire feeder from the main service panelboard. At the panelboard in the garage you can either install a main disconnect for the garage or use a main service breaker protected panelboard. You can also use a Main Lug Panelboard as long as up to six switches (breakers) will kill all power to the panelboard.

Finally, the grounding system at the garage must be isolated from the Neutral at the garage panelboard. No Neutrals can connect to the grounding buss bar and no equipment grounding conductors can connect to the Neutral buss bar.

Don, the OP is not in the US.

I knew that based on your original response. I just wanted t show the general overview for setting this up in the U.S.A.