<p>The rising cost of servicing the UK national debt pushed up borrowing last month</p><p><strong>How much ‘headroom’ might John Healey still have to keep within the government’s fiscal rules?</strong></p><p>That’s the question dogging Westminster and the City.</p><p>“The chancellor has probably lost about half the headroom he inherited, leaving it between £10bn to £15bn. As long as the headroom is in double figures, he will probably be able to avoid topping it up, but the drop in headroom means