LONDON—Britain is reviewing the idea of vaccine certificates to allow access to travel, hospitality, and entertainment and discussing the best way to proceed in terms of fairness, said Kwasi Kwarteng the secretary of state for business, energy, and industrial strategy. P&O Cruises said on Tuesday that it would only accept as passengers those who have had both doses of the vaccine for its trips around the UK this summer, sparking a fresh debate on the issue. When asked about the fairness of companies requiring proof of vaccination to grant entry and what the government’s stance was on the matter, Kwarteng said it was under review. “We are discussing what the best way to proceed is,” Kwarteng told the BBC. More than half of Britain’s adult population will have received the first shot of a COVID-19 vaccine by the end of the week. Kwarteng said there were two separate issues, that of …