The FA says it was only made aware of the full details of the report into Sampson’s conduct at Bristol Academy last week despite the allegations first being made in March 2014.
Sampson left Bristol in 2013 to take charge of England, which finished third at the 2015 Women’s World Cup.
The FA says it believes there is “clear evidence of inappropriate and unacceptable behaviour by a coach.” The FA refused to disclose more details of the allegations but stressed no laws were broken.
FA chief executive Martin Glenn says “during his time at Bristol, Marc had overstepped the professional boundaries between player and coach.”
FA chairman Greg Clarke added “we know coaches are in a potential position of power and that position mustn’t be abused.”
Eni Aluko complaint
Sampson’s position at the helm of the Lionesses has been under scrutiny since a complaint from striker Eni Aluko.
Aluko is the former England player whose allegations of racism, harassment and bullying sparked an investigation into Sampson’s alleged conduct.
Sampson, who was named England boss in March 2015, has been cleared twice, by a Football Association review and an independent investigation, and he firmly denies any wrongdoing.
England’s players rushed towards him to celebrate the opening goal in Tuesday’s 6-0 World Cup qualifying win over Russia.
Every member of the starting XI raced to the bench after Nikita Parris netted the 11th-minute opener.
Sampson said of being mobbed by the dugout: “I didn’t foresee anything coming really, in terms of that.”
He said it was “not something that is usual” as he lavished praise on his players, for whom further goals came from Jodie Taylor, Jordan Nobbs, Lucy Bronze and Toni Duggan, who struck twice in the second half.
Questioned further about the team’s response to him, in the first game since the allegations against him became public knowledge, Sampson added: “Our initial joy is that we’ve scored the opening goal in a big World Cup qualifier.
“We’ve really preached team togetherness and support for your team-mates since I’ve come through the door. It’s not something that is usual and it was something different but it’s a quality we’re always pushing with the players.
“It has been a difficult time for everyone, that’s for sure. This has not been an easy situation and it is a serious situation, and we’ve tried our best to be as respectful as we possibly can towards that, but be fully aware that we’ve got a job to do.
“These women are representing their country tonight and they wanted to make sure their level of performance was right and their attitude was right.”