Large supplies are really unnecessary unless you run a bunch of electric showers and other huge loads. Cookers and hobs have the option of connecting them to 3 (cookers) or 2 phases (most hobs), as do all larger electric water heaters and instant showers. I've heard of people who successfully managed to live with a 25 A 3-phase supply, a free-standing electric cooker and a 21 kW electric shower without ever blowing a main fuse! That's an extreme case and it was probably sheer luck for them but 35 A 3-phase already provides a lot of power. If you've got a gas cooker/hob and a combi boiler or central heat and hot water you're extremely unlikely to exceed a total load of 5 kW in my experience!
