Thanks for the reply, I actually meant to write
"1 phase of 3 to get 230v mains you mustn't have a load on the other 2 phases otherwise the load will be unbalanced over all 3 phases."
You have to remember that it is not just one house but many so there are many on each phase and they will average out.

For three phase to run correctly they must all balance out. (I am not having go)

Regarding the oven I believe there are some that run from a 13A socket these days.