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From early in his leadership, allegations of anti-Semitism in Jeremy Corbyn's Labour party grew.

From early in his leadership he promised he would do everything to stamp it out.

But from early in his leadership, he faced accusations of not taking the problem seriously enough.

All of this in a culture of suspicion between different factions in the Labour Party, and very deep hostility.

But the testimony Panorama reveals tonight - and the leaked emails they have obtained - will paint a picture that contrasts with the leadership's claims that they are doing as much as they can.

And they will cause deep alarm in many parts of the Labour movement.

For their part, Mr Corbyn's allies totally reject the testimony that's been put forward - instead claiming those who have come forward are "disaffected".

But this is a real challenge to Mr Corbyn's handing of anti-Semitism.

Labour has already lost several MPs and members of the Lords over these concerns.

If they fail to get a grip on it, what might they lose next?