LABOUR were relieved to discover that milord Sewel of Coke, who has been all over the tabloids allegedly cavorting with prostitutes, had resigned his Labour Party membership some time ago when he became deputy speaker of the Lords.

However, he remains “a non-affiliated member” so he could still be voting in the Labour leadership contest. Indeed, the ladies of the night, who he allegedly entertained, might also be voting for the Labour leader.

After all, they seemed very interested in his Lordship’s views on all the candidates in Labour's election. And all they needed to do was put up £3, register as a supporter to have their say.

Labour even emailed me asking me to vote in their election as a supporter. I was tempted – I was involved with the Labour Party many years ago – but I've never been a member of any political party since then.

I thought at the time that Labour were asking for trouble inviting anyone and everyone to vote for their next leader. The party was trying to break out of it's political ghetto.

The registered supporters arrangement is loosely modelled on US primaries, where just about anyone can get involved in the early rounds of selecting candidates for US presidential elections. The French socialists have a similar system.

Labour wanted to bring in new blood who would galvanise and renew their party. That's exactly what they got – tens of thousands of them. Mostly young and mostly minded to vote for Jeremy Corbyn.

This wasn't in the script and right wing Labour MPs like John Mann have reacted in horror. Turns out that one member one vote is only democratic so long as members vote the right way.

Claims have been made by that the Trotskyite Militant Tendency, which no longer exists, has been conducting an orchestrated campaign of “entryism”. Unite has been accused of telephoning its members and urging them to register. Which is of course perfectly within the rules.

But I bet most of the new Labour members have barely heard of Leon Trotsky. Like Che Guevara, whose image has been appropriated by the comedian Russell Brand, the Russian revolutionary is an obscure historical figure to most people under forty, notable only for Stranglers song about how he was murdered with an ice pick, courtesy of Joseph Stalin.

Labour's panic is somewhat hilarious because the policy of one member one vote was supposed to immunise it from entryism and from trades union domination. When Ed Miliband introduced OMOV last year he fulfilled a right-wing aspiration that goes back to Roy Jenkins and the Gang of Four in the 1980s.

Militant Tendency as it was in the 1980s had made various attempts to seize control of moribund Labour constituency parties. The trades union barons used to wield at conference massive bloc votes of their members whether they'd been consulted or not. OMOV was supposed to put ordinary Labour members back in charge.

But only if they are the right kind of members. Labour's interim leader, Harriet Harman, seemed seriously to be entertaining the idea of calling a pause Labour's leadership election so they could check for reds under the beds.

“People who don't subscribe to the aims and values of the Labour party” she said. “should not be allowed to elect the leader”. This raises the interesting question of what Labour's aims and values actually are.

Labour already has a membership vetting process which is designed to do root out fraudulent or malicious applications. Only 700 have so far been rejected.

What is Ms Harman planning to do now? Only allow people to join the party if the sign a pledge not to support a left wing candidate?

They should have taken a leaf out of the SNP's book. Its membership has more than quadrupled since the referendum, but they didn't go looking for reds under the bed or unionist spies.

The SNP welcomed the new members with open arms. They even waived their rule that new members must wait a year before they can stand as general election candidates.

An invasion of new members is something of which Labour should be proud, even if there are a handful of silly Telegraph readers who've registered to create mischief. It's exactly what the party needs.

Labour is supposed to be a party of the left. If it tries to bar members from participating because they are socialists, then the party is over.