The government’s borrowing costs have risen to their joint highest level since the 2008 financial crisis, after a sharp jump in the oil price prompted a sell-off in UK debt because of concerns over inflation. The yield on the 10-year gilt – the main benchmark for any government’s long-term ability to borrow – climbed back above five per cent for only the third time since the Iran war broke out on Tuesday, laying bare the extent to which Britain is almost uniquely exposed to the ongoing energy shock. The UK’s government…