Board of Deputies senior vice-president, Laura Marks, who represents the Movement for Reform Judaism, has joined the United Synagogue.
Ms Marks, who has become an associate member of Highgate Synagogue while retaining links with the Reform Alyth, said, "Lots of people are members of more than one synagogue. One of the things I'm most passionate about is bringing the community together."
The Mitzvah Day founder's move has come ahead of next spring's Board presidential election, which she is widely expected to contest. All her fellow officers who are eligible to stand, vice-presidents Jonathan Arkush, Alex Brummer and treasurer Laurence Brass, belong to the US.
"If I'm to understand the US better," she said, "I realised I could no longer sit on the outside." She could have simply gone along to Highgate without joining "but I think if you want to be part of something, you have to contribute.
"Were I to stand for president, I would have to speak for the whole of the mainstream community and that is an issue I take very seriously."