UK's Helios Towers rises after authorising additional $100 million buyback
** Shares in telecom infrastructure group Helios Towers HTWS.L rise 3.8% to 210 pence
** Co authorises an additional $100 million share buyback, increasing the programme's total size to $175 million
** Extends expected completion date by one year to December 31, 2027
** Stock up ~25% YTD