> UK is 400v phase-phase and 230v phase-neutral. The distribution transformers are three-phase out and the LV main serving a street is 3 phase wires and a neutral, each house is fed from one of the phases and connected to the neutral.

Good to know.

> My understanding of the standard US system is that the distribution transformer is fed with one phase, the secondary side of the transformer has a centre-tap neutral and two live phases which have 120v to neutral and 240v phase-phase.

yes