Purtin knows the UK has no middle rung on the escalatory ladder, says Frank Gardner, right (Image: Getty)Veteran BBC Security Correspondent Frank Gardner has admitted to testing the Arabic of “impressive” new MI6 boss Blaise Metreweli – and says she passed with flying colours. “I’m sick of people saying, ‘Oh, so-and-so’s Arabic is really good, and it turns out they can count from one to ten and that’s it,” chuckles Gardner, who is himself fluent. “But she learned it through total immersion in the Middle East – the right way to do it.”Metreweli became the first female head of the…