By Richard Norton-Taylor and Nicholas Watt in The Guardian - Boris Johnson has placed himself at the head of cross-party group, including a former Tory attorney general and a Labour leadership contender, who are calling on Barack Obama to secure the release of Shaker Aamer, the last British resident held in Guantánamo Bay. In an intervention timed to coincide with US Independence Day, six former cabinet ministers have joined leading writers, actors, directors, musicians to warn the White House that the continued detention of Aamer is undermining US standing in the world. The Saudi-born Aamer was seized by bounty hunters in Afghanistan and handed over to US forces in December 2001. Two months later, he was rendered to the US military prison on Cuba. US authorities have made it clear that they have no intention of charging him.