That only applies to water bills, and if I remember correctly the reason why that rule exists is that the UK was starting to have cholera outbreaks before it was put into place. Usually, I think electricity suppliers here deal with people who don't pay their bills by forcing them onto prepayment meters that require them to pay up front for it and automatically cut them off when the money runs out. So technically they're not disconnected entirely, but they sure aren't getting electricity unless they pay for it.