This month should be a triumph for Chief Rabbi Ephraim Mirvis.His flagship event, Shabbat UK, is now established in our calendar and, this weekend, the community will unite in celebration .

It's a shame, then, that October is marred by an unfortunate and alarming episode, which casts serious doubt over the Chief Rabbi's judgment and the direction in which he is taking the United Synagogue.

I refer to the "confidential" letter sent to United Synagogue rabbis and shul chairs, warning against "offer[ing] a platform to speakers who are inappropriate".

Who does he consider "inappropriate"? What prompted this intervention?

He is clearly hinting at something significant - but the Chief Rabbi won't come out with it.

He rather suggests that rabbis who can make neither head nor tail of this cryptic and vaguely threatening letter should contact his office.

If the Chief Rabbi has something to say, he should have the courage of his convictions and explain what he means.

Most have concluded that the letter was prompted by the appointment of Dina Brawer as scholar-in-residence at Hampstead Synagogue.

Rebbetzin Brawer is the UK ambassador for the Jewish Orthodox Feminist Alliance, and the first UK student to enrol at New York's Yeshivat Maharat, which ordains Orthodox women as spiritual leaders.

Asked by the JC directly whether the letter concerned Rebbetzin Brawer, the chief rabbi's office declined to comment. Nor would they welcome Rebbetzin Brawer's appointment.

The silence speaks for itself.

What, then, is Rebbetzin Brawer's sin?

Rebbetzin Brawer is an impeccably Orthodox woman of great Jewish learning. For 15 years, the United Synagogue was perfectly happy to have her as rebbetzin of two of its communities, Northwood and Borehamwood.

However, in recent years she has become associated with the two words that apparently frighten our allegedly Modern Orthodox chief rabbi like no other: "Orthodox feminism".

Orthodox synagogues across the United States are appointing women to their clergy teams; in Israel, Efrat's chief rabbi, Shlomo Riskin, is ordaining women as halachic authorities. Here in the UK, they are apparently "inappropriate".

But it's not just about women, and certainly not just about Dina Brawer.

Those "who represent a hashkafa [outlook] which encourages practices which run contrary to our normative United Synagogue approach" are all to be blackballed.

Somehow, no one imagines that the Chief Rabbi is referring to people to the right of him - although Charedim answer his definition perfectly. It's about the left.

Over decades, the US beth din (which, the Chief Rabbi's letter says, was party to his warning), has attempted repeatedly to ostracise any but the most Orthodox views - and totally failed.

Their approach is not that of the United Synagogue membership, which wants a broad church, and which is not interested in having Charedi standards imposed on them.

There should be room for every congregation to develop its own vision.

Yet, Canute-like, the Beth Din, and now apparently the Chief Rabbi, likely pressed by some of his pulpit rabbis, seem to believe that, if only they forbid left-wing voices from being heard, they will magically disappear.

This was a mistake in the Jacobs affair; a mistake in the Limmud "ban"; and a mistake when they forced Jonathan Sacks to change the text of The Dignity of Difference.

Now, too, the best way to encourage the growth of the Orthodox left is to attempt to ban and suppress it. (So thanks, guys!)

This attempt at thought control shows great insecurity, as well as insensitivity to the increasing swathe of United Synagogue members who feel uncomfortable with parts of the US framework.

Chief Rabbi Mirvis, when appointed, was meant to be the ''people's rabbi'', the champion of the common US member.

His reputation, in this regard, has just taken a great hit.