The support comes after RFU chief executive Bill Sweeney had already publicly reaffirmed confidence in Borthwick in the immediate aftermath of their defeat to Italy, insisting he still had the backing of the union's leadership.
Borthwick took charge of England in December 2022 and has since guided them to a Rugby World Cup semi-final. However, he is still without a Six Nations title during his tenure, with results in the annual tournament continuing to fall short of expectations.
In a statement, the RFU said: "Following the conclusion of the Guinness Men's Six Nations, the RFU, with the support of external independent contributors, has completed a detailed and robust review of the campaign, informed by players, coaches and the wider back-room team.
"The process included a series of in-person one-to-one conversations, enabling open, constructive and, at times, challenging discussions.
"These conversations, along with other insight, helped ensure the review was grounded in honesty and a focused assessment of where things didn't go well across the Championship.
"The review concluded that, despite coming off a 12-game winning run, England's underperformance across the Six Nations was not the result of a singular failure or issue.
"The process included a series of in-person one-to-one conversations, enabling open, constructive and, at times, challenging discussions.
"These conversations, along with other insight, helped ensure the review was grounded in honesty and a focused assessment of where things didn't go well across the Championship.
"The review concluded that, despite coming off a 12-game winning run, England's underperformance across the Six Nations was not the result of a singular failure or issue.
"We recognise why supporters felt frustrated and that they expected more. That disappointment was shared internally, and it underpinned the seriousness with which everyone engaged in this process.
"England head coach Steve Borthwick has engaged in the review with honesty and rigour, and he and his coaching team are already addressing issues identified."
Commenting further, Sweeney added: "This has been a thorough and honest review, and it is clear that improvement will come from addressing several areas rather than chasing one simple answer.
"We've all seen what this England side is capable of - most recently in the performance against France, and during the strong winning run before that.
"That doesn't disappear overnight. The challenge now is delivering that level consistently, and we are confident this group can do that, supported by the insight and feedback this review has surfaced.
"This is a young England team that is still growing and developing, and we understand progress in international sport is rarely linear.
"Steve has engaged in this process with full openness and has clear plans in place to address these findings. We are all behind him and his coaching team going into the Nations Championship and the series of matches leading into Rugby World Cup 2027."