As a dead cat, Alastair Campbell has proved most effective. You’ll recall the advice of the rightwing election guru Lynton Crosby, who recommended that a politician about to face a scandal or crushing revelation throw a dead cat on the table: onlookers might be appalled, even disgusted – but at least you’d have changed the subject.

Tom Watson calls Alastair Campbell's expulsion 'spiteful' Read more

On Tuesday, confirmation came that the Equality and Human Rights Commission is to investigate the Labour party over anti-Jewish racism. That is a very big deal. Only one political party has come under EHRC scrutiny before, and that was the BNP. It should be a day of shame that an organisation that likes to boast that combating prejudice is in its DNA is now under investigation for that very offence. And make no mistake: the EHRC does not make such a move lightly. It only rarely undertakes a full-scale investigation (the last comparable inquiry was into the Metropolitan police several years ago). Human rights lawyers who work closely with the EHRC say the commission would not launch a full investigation into Labour unless they had seen evidence of institutional racism that was “credible and serious”.

So how to bury this particular piece of bad news? The answer appears to have come in the form of Tony Blair’s former director of communications, and his expulsion from the Labour party. That story promptly knocked the EHRC inquiry down the running order and gave supporters of the leadership a hate figure to attack: “Alastair Campbell’s ‘sexed up’ dossier started the Iraq war and left a million dead,” tweeted Momentum, apparently forgetting the minor supporting role played by George W Bush and the United States military. “Being kicked out of the party is the least he deserves”. All so much more fun than having to bow your head in shame at the realisation that your movement now stands alongside the BNP in the category of political parties deemed to merit statutory investigation for racism.

Still, if that was a deliberate tactic of news management – with Campbell more spinned against than spinning – it came at a cost. For one thing, it invited an obvious comparison. How striking that Labour was able to move so swiftly against Campbell – with expulsion coming less than 36 hours after his admission of voting Lib Dem – when it had taken two years or more to expel party members guilty of anti-Jewish racism or, just as often, failed to expel them at all. MPs stepped forward to wonder why it was that Holocaust deniers were still members of their local Labour party, months and years after they’d been reported, while Campbell had been so rapidly ejected. A party’s disciplinary actions tell you a lot about their priorities, and what this says is that Labour regards a protest vote against Brexit as a greater crime than spreading neo-Nazi hatred.

The defence is that Campbell’s case was straightforward, because support for another party is punished by “auto-exclusion”, automatic expulsion with no need for any legal process. Trouble is, that’s not quite right. Labour’s former head of compliance, Mike Creighton, who knows the Labour rule book better than most, explained that “Announcing after the polls closed that you voted for another candidate does not breach the rules in any way. Voting for another party is not in itself a breach of rule however much people wish it were.”

That rather undermines the defenders of Campbell’s expulsion who have been arguing that the move was not some cunning bit of politicking by Team Corbyn, that it was barely a deliberate decision taken by a human being, but rather was done almost automatically, as if by an algorithm. Their goal is to make “auto-exclusion” seem like a universal rule, consistently applied, regardless of whether the rule-breaker was straying to the left or right.

But, again, the facts stand in the way. Witness the letter to the Guardian recalling the thousands of Labour party members who voted against the party’s official candidate in the 2000 London mayoral election, Frank Dobson, preferring to vote and actively campaign for Ken Livingstone, who ran as an independent. Did the hated Blair, the control freak’s control freak, issue those rebels with instant auto-exclusion notices? No, he did not. They faced no sanction whatsoever.

And yet Labour officials confidently insisted yesterday that “publicly declaring or encouraging support for another candidate or party is against the rules and is incompatible with party membership.” That will have come as news to one party member who tweeted what looked a lot like a warm declaration of support and encouragement for “another candidate or party” back in 2012. The candidate in question was George Galloway, who had just defeated Labour in a byelection in Bradford West. The message of support was effusive: “Congratulations to George Galloway on astonishing result in Bradford. Big message here on opposition to wars and austerity.” Who wrote that tweet? Why, it was none other than one Jeremy Corbyn. Needless to say, he did not receive an auto-exclusion notice either.

The truth is, this is displacement activity. Labour can debate expulsions and begin purges in a quest for ideological purity – or it can face the reality: namely, that it was just trounced in a UK-wide election, reduced to 14% even when taking on the most divided, incompetent and discredited government of modern times; that it came third in Wales and fifth in Scotland. It can punish the lifelong supporters who voted for other parties out of a desperate desire for someone, anyone, to oppose the calamity of Brexit – but, if it chooses that path, it should brace itself for the consequences. As Kevin Maguire of the Mirror puts it, “Expel every Labour member who voted Lib Dem or Green last week and Labour will shrink from Europe’s largest political party to one of the smallest”.

It can kick out Campbell. It can even kick out the many other Labour members now stepping forward, Spartacus-style, to admit that they too broke ranks last Thursday. Or it can ask itself why those devoted supporters felt compelled to break the habit of a lifetime – and do what’s needed to bring them back.

• Jonathan Freedland is a Guardian columnist