It was a punishing general election defeat; the fourth in a row and Labour's worst performance, in terms of seats, since 1935.

It went deeper than that because the party saw its once loyal supporters switch to the Tories, yes the Tories, in areas that had elected Labour MPs for decades, in some constituencies for nearly a century.

Today's letter to The Observer, signed by some of those former MPs who lost their seats in former heartlands, reads like a warning.

There's a fear amongst those MPs, who are regarded as being either centrist or on the right of the party, that the panel, including former leader Ed Miliband, set up to review why Labour was defeated will produce a whitewash.

The Labour leader during the general election campaign. Credit: PA

Read this line from today's letter: "We need to be honest about why our outgoing leadership’s reflexive anti-western worldview was so unpopular and address the reasons."

And the implication that can be drawn is that they worry the internal inquiry will not be honest about the reasons for the losses.

The blame lies with the Corbyn leadership, that's the clear conclusion from this group of former MPs who also claim that “cronyism at the top of (the) party and repeated unwillingness to stand up to the stain of anti-Semitism” was another major factor in the defeat.

Jeremy Corbyn during the general election campaign. Credit: PA

With the key governing body, Labour's National Executive Committee, controlled by his allies and the membership largely seen as supportive, Jeremy Corbyn and 'Corbynism' still dominate the internal mechanisms of the party.

The group of MPs writing today are concerned that an "unflinching" inquiry into what went wrong will not be possible with the reins of the party still in the hands of the Leader who oversaw such crushing losses.