LONDON (Reuters) - Britain opened order books on Tuesday for the sale of several billion pounds' worth of a new government bond maturing in October 2061, one of the bookrunners involved in the syndication said.The 0.5% 2061 gilt is initially priced to yield the same or 0.5 basis points more than the 4% January 2060 gilt .The launch of a new 10-year gilt via syndication last week - part of the government's planned surge in borrowing to help pay for its coronavirus response programme - drew..