By Elizabeth Piper and Andrew MacAskill BIRMINGHAM, England (Reuters) – British Prime Minister Liz Truss tried to reassure her party and the public on Sunday by saying she should have done more to “lay the ground” for an economic plan that saw the pound fall to record lows and government borrowing costs soar. On the first day of her governing Conservative Party’s annual conference, Truss, in office for less than a month but already under intense pressure, sought a softer tone by saying she would support the public during a difficult winter and beyond. She defended her “growth plan”, a package …