HM Revenue and Customs (HMRC) has not ruled out following through with its initial plan to close self assessment tax return helplines for six months each year, the boss of the tax office has said. Jim Harra, HMRC’s chief executive, could attempt to close its helplines again despite an outcry over previous plans. In March, the tax office announced that from April 8 until September 29, taxpayers would have been unable to call HMRC for help with their self assessment tax return. However less than 24 hours later, they made a drastic U-turn after backlash from MPs and trade bodies, who warned taxpa…