By Iain Withers, Sinead Cruise and Lawrence White LONDON (Reuters) – While British households head into a winter of soaring energy costs, a tumbling currency and nearly double-digit inflation, the country’s banks are in line for a handsome payday as mortgage prices spike after a decade of stagnation. Banks are finding the home loan market stacked in their favour after years of low mortgage rates, but are also aware that bigger mortgage bills could spell trouble for cash-strapped customers. Some investors and analysts are already questioning whether banks’ risk models are up to the task of iden…