Borthwick (left) has come under pressure a little less than a year after Sweeney (right) survived a grassroots rebellion aimed at ousting him from his role There are no guarantees on the future of England coach Steve Borthwick until a review into this year's dismal Six Nations campaign reports back at the end of April, says Rugby Football Union boss Bill Sweeney. England lost four of their five games, their worst performance since the tournament was expanded in 2000. While a post-Six Nations review is standard practice regardless of how England perform, Sweeney admitted results this year required a "deeper dive" into an "unusual outcome". "Clearly, there are some issues and we're getting to them already to see what needs addressing," said chief executive Sweeney when asked whether Borthwick would definitely be in place for England's matches against South Africa, Fiji and Argentina in July.…